Self-assembled hollow microspheres poly(o-chloroaniline) (POC) have been synthesized by simple oxidative polymerization of o-chloroaniline using camphor-sulfonic acid (CSA) as dopant acid and ammonium persulfate (APS) as oxidant. The POC microspheres were characterized by means of FTIR, XRD and SEM analysis. Adsorption characteristics of POC spheres were studied by using methyl orange (MO) as adsorbate. It was found that adsorption of MO by POC was better described by pseudo-second-order kinetics than any other kinetic model, such as the pseudo-first-order and intra-particle diffusion models. Langmuir adsorption isotherm model was the best to fit experimental data. The results showed that hollow microspheres of POC can be used as novel and low-cost adsorbent for removal of organic dye from waste water.

Direct evidence was first demonstrated for the oxidative degradation of decabromodiphenyl ether (BDE209) in aqueous TiO2 dispersions under UV irradiation (λ > 340 nm). BDE209 was hardly debrominated over TiO2 in UV-irradiated acetonitrile dispersions, but the addition of water into the dispersions greatly enhanced its photocatalytic oxidative debromination. The debromination efficiency of BDE209 as high as 95.6% was achieved in aqueous TiO2 dispersions after 12 h of UV irradiation. The photocatalytic oxidation of BDE209 resulted in generation of aromatic ring-opening intermediates such as brominated dienoic acids, which were further degraded by prolonging UV irradiation time. The photocatalytic oxidative debromination of BDE209 was further confirmed by the observation that the BDE209 degradation in water–acetonitrile mixtures with different water contents was positively correlated with the formation of •OH radicals, but not photogenerated electrons. The use of water not only avoided the scavenging of reactive radicals by organic solvent but also enhanced the adsorption of BDE209 on the surface of TiO2, both of which favor the contact of BDE209 with photogenerated holes and •OH species. The confirmation of efficient oxidative degradation and debromination of BDE209 is very important for finding new ways to remove polybrominated diphenyl ethers from the environment.

The degradation of organic pollutants was conducted by using persulfate as the oxidizing agent and ferrous hydroxide colloids as a heterogeneous activator. Complete degradation of sulfamonomethoxine (SMM, 0.06 mM) was achieved within 1 min in the presence of persulfate (1.2 mM) and ferrous hydroxide colloids (1.2 mM), and the apparent rate constant in this system was as high as 2.21 min−1, being 5.3 times of that using Fe2+ ion (0.42 min−1) as the homogeneous activator at pH 3.0. The colloidal activator was also much superior to Fe3O4 nanoparticles, which were reported as good activator of persulfate and provided an apparent rate constant of 1.09 min−1 under similar conditions. The combination of persulfate and ferrous hydroxide colloids also caused efficient degradation of Rhodamine B and 4-nitrophenol with high total organic carbon (TOC) removal. The highly efficient activation effect of the colloids is attributed to the intrinsic nature of colloid particles with large specific surface area, which simultaneously increase the chemical attack possibility of persulfate and the adsorption of organic pollutants on the colloidal surface. The highly efficient activation effect, easy preparation and use allow promising applications of the ferrous hydroxide colloids in removing recalcitrant organic pollutants with persulfate as green oxidizing agent.Highlights► Ferrous hydroxide colloids were characterized as efficient activators of persulfate. ► Use of persulfate and ferrous hydroxide colloids caused fast degradation of pollutants. ► Ferrous hydroxide colloids were superior to Fe3O4 and Fe2+ as persulfate activators.

•The reduction of graphene oxide affected its surface chemistry, aggregation and conductivity.•The use of reduced graphene oxide was successfully used for preparing RGO/PANI composites.•The RGO/PANI composite exhibited high capacitances and good cycling stability.•A proper load of PANI was required for high capacitances and good rate performance of the composite.Reduced graphene oxide (RGO) was compounded with polyaniline (PANI) to prepare supercapacitor electrode materials. For the preparation, graphene oxide (GO) was reduced with glucose and ammonia, and then PANI was in situ deposited onto the RGO nano-sheets by polymerizing aniline with ammonium persulfate (APS) as oxidizing agent. The obtained composites were characterized with scanning electron microscope, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy (EIS). It was found that with increasing reduction time, the oxygen content on the surface of GO was decreased, leading to increased ID/IG ratio in the Raman spectra of GO and increased conductivity of GO. Consequently, the capacitance properties of RGO/PANI composites could be significantly improved by the reduction of GO. It was also observed that the initial concentrations of aniline being used for the polymerization could influence the rate performance of the composite. Under the optimal preparation conditions (the reduction time of graphene 60 min, the initial concentration of aniline 0.025 mol L−1, and the molar ratio of aniline to APS 1:1), the obtained composites exhibited a specific capacitance as high as 1045 F g−1, along with a retention of 97% after 1000 cycles.The reduction of graphene oxide improved significantly the capacitance of RGO/PANI composites.

Composites of polyaniline (PANI) and graphene oxide (GO) were prepared in the suspension of GO in the presence of aniline and H2O2 in acidic media. Open-circuit potential measurements confirmed that the simultaneous use of GO and H2O2 made the polymerization of aniline faster and more effective than using GO or H2O2 alone. SEM observation showed that PANI nanoparticles were deposited on GO sheets with uniform and well-arranged morphology. It was found that there were considerably strong interactions between GO and PANI chains in the composites. Along with the cyclic voltammetric properties of typical PANI, the composites exhibited a capacitance as high as 797 F g−1 with a good stability during long-term cyclic voltammetric measurements, which was attributed to the uniform arrangement of PANI nanoparticles on GO sheets, leading to improved charge transport in the composites.Graphical abstractGraphene oxide/PANI composites were synthesized by growing PANI nanoparticles on graphene oxide sheets. The composite exhibited high capacitance and long-term stability.Highlights► GO/PANI composites were prepared by polymerizing aniline on GO sheets. ► The activation of monomers by GO was important in the synthesis of the composite. ► The simultaneous use of H2O2 and GO improved the growth of PANI on GO surfaces. ► The composite exhibited high specific capacitance and energy density. ► The composite had good long-term stability with capacitance retention of 118% after 500 cycles.

A molecular imprinted polymer (MIP) sensor was fabricated by directly eletropolymerizing monomer o-phenylenediamine in the presence of template chlortetracycline (CTC), based on controlled electrochemical reduction of graphene oxide (GO) at cathodic potentials. In comparison with GO, the reduced GO (RGO) increased the cyclic voltammetric peak currents of [Fe(CN)6]3−/[Fe(CN)6]4− redox pair by a factor of about 300%, which was influenced by the amount of used GO and the reduction time. Integrating the excellent response amplification of RGO and the special recognition of MIP, the new MIP sensor was used to detect CTC indirectly by using [Fe(CN)6]3−/[Fe(CN)6]4− redox pair as an electrochemical probe. The electrochemical performances of the sensor were evaluated with cyclic voltammetry and differential pulse voltammetry (DPV). The MIP sensor exhibited a wide-range linear correlation between the peak current variation (ΔI) of the DPV cathodic peak and the concentration of CTC in the range of 10.0–500.0 μM. The use of the RGO-based MIP sensor gave satisfactory results in the analysis of tap water and laboratory wastewater samples.

Molecular imprinting technology allows synthesis of polymers with specific recognition ability towards target pollutants, which show potential to selectively remove Highly Toxic Organic Pollutants (HTOPs) in the presence of common organic matrices that are thousands of times more abundant than the targets. This feature article summarizes the current development of molecular imprinting for removing HTOPs from polluted water, with a special emphasis on the application of molecularly imprinted polymers to improve the efficiency of photocatalytic and biological degradation of HTOPs in wastewater.

By using cobalt nitrate and bismuth nitrate as precursor salts and NaOH as a precipitation agent, Co3O4–Bi2O3 nanocomposite oxides (CBO) were prepared as a heterogeneous catalyst for the activation of peroxymonosulfate (PMS) by a conventional reverse co-precipitation method and post-calcination. The characterization with transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and Raman spectroscopy demonstrated that there was a strong interaction between Bi and Co components in CBO. The presence of Bi increased the content of surface hydroxyl oxygen, which favored the formation of Co(II)–OH complexes that were vital for heterogeneous activation of PMS. CBO showed strong catalytic activity in the heterogeneous activation of PMS for degradation of organic pollutants such as methylene blue (MB), rhodamine B, phenol and 2,4-dichlorophenol. With the addition of 0.5 mmol L−1 PMS, CBO produced fast and full degradation of MB (20 μmol L−1) with the apparent rate constant of 0.36 min−1, being 8.6 fold of that (0.042 min−1) over nano-Co3O4. It decreased the cobalt leaching to 43 μg L−1, being much less than that (158 μg L−1) from Co3O4 under the same conditions. The effects of CBO loading, PMS concentration and calcination temperature on the degradation of MB and cobalt leaching were also investigated.

The effect of EDTA on the H2O2 activation ability of Fe3O4 nanoparticles was investigated for removing organic pollutants. Regular Fe3O4 nanoparticles were observed to have moderate catalytic activity, which was not suitable for the degradation of various organic pollutants. The addition of EDTA enhanced the activation of H2O2 on the surface of Fe3O4 nanoparticles, thereby accelerating the formation of reactive oxygen species and increasing the degradation rates of pentachlorophenol, sulfamonomethoxine, and Rhodamine B by 84.4, 48.3, and 17.5 times, respectively, at pH 5.0 and 40 °C. Based on spectroscopic and density functional theory studies, adsorption mechanisms for H2O2 and EDTA on the surface of Fe3O4 nanoparticles were proposed. It was clarified that the enhancing effect of EDTA was attributed to an appreciable improvement of Fe3+/Fe2+ recycling on the surface of Fe3O4 nanoparticles, and to the simultaneous degradation of EDTA and target pollutants.

Effects of chelating agents on the catalytic degradation of bisphenol A (BPA) was studied in the presence of BiFeO3 nanoparticles as a heterogeneous catalyst and H2O2 as a green oxidant. The oxidizing ability of H2O2 in the presence of nano-BiFeO3 alone was not so strong to degrade BPA at neutral pH values, due to the limited catalytic ability of nano-BiFeO3. Once the surface of nano-BiFeO3 was in situ modified by adding proper organic ligands, the BPA degradation was much accelerated in the pH range of 5–9. The enhancing effect of the ligand was observed to have an order of blank < tartaric acid < formic acid < glycine < nitrilotriacetic acid < ethylenediaminetetraacetic acid (EDTA). The addition of 0.25 mmol L–1 EDTA in the H2O2–BiFeO3 system at pH 5.0 and 30 °C increased the BPA removal from 20.4% to 91.2% with reaction time of 120 min. The enhancing effect of the ligand was found to be indifferent of the possible dissolution of iron from nano-BiFeO3, but correlated well with the accelerated •OH formation from the H2O2 decomposition at the BiFeO3 surface, which was confirmed by ESR measurements and density functional theory studies. In general, more addition of EDTA, higher H2O2 concentrations, or higher temperatures were favorable to the BPA degradation. The effect of the EDTA addition on the kinetics of BPA degradation was also clarified.Keywords: BiFeO3; bisphenol A; catalytic degradation; ligand; surface modification;

A novel method was developed to synthesize graphite oxide/TiO2 composites as a highly efficient photocatalyst by in situ depositing TiO2 nanoparticles on graphene oxide nano-sheets by a liquid phase deposition, followed by a calcination treatment at 200 °C. The two-dimensional porous graphene oxide/TiO2 composites had specific surface area of 80 m2 g−1 being considerably larger than that of P25 and the similarly prepared neat TiO2 particles without using graphene oxide. The composites exhibited excellent photocatalytic activity, being influenced by post-calcination temperature, graphene oxide content and solution pH. Under optimal conditions, the photo-oxidative degradation rate of methyl orange and the photo-reductive conversion rate of Cr(VI) over the composites were as high as 7.4 and 5.4 times that over P25, respectively. The excellent enhancing effect of graphene oxide nano-sheets on the photocatalytic properties of TiO2 was attributed to a thin two-dimensional sheet support, a large surface area and much increased adsorption capacity, and the strong electron transfer ability of the thermally reduced graphene oxide in the composite.

A simple ultrasound-assisted co-precipitation method in combination with a calcination treatment was developed to prepare magnetic Mg–Al layered double hydroxides composite as an adsorbent material to remove fluoride ions from aqueous solutions. The application of ultrasound in the preparation process promoted the formation of the hydrotalcite-like phase and drastically shortened the time being required for preparation of the crystalline composite. It was found that the ultrasound irradiation assistance decreased the size of the composite particles and increased the specific surface area, being favorable to the improvement of the adsorption capacity. The composite prepared under the ultrasound irradiation exhibited fairly high maximum adsorption capacity of fluoride (47.7 mg g−1), which was 60% higher than that of the composite prepared without the ultrasound irradiation assistance with the same aging time. The thermodynamic and kinetic studies demonstrated that the adsorption of fluoride ions involved the reconstruction of the layered structure in the composite. In addition, the magnetic composite can be effectively and simply separated by using an external magnetic field, and then regenerated by desorption and calcination.► Magnetic Mg–Al layered double hydroxides were prepared by a sono-assisted method. ► The newly developed composites exhibit high efficiency for fluoride removal. ► The adsorption of fluoride involves the reconstruction of the layered structure. ► The used adsorbents can be recovered and reused for removing fluoride ions.

Persulfate can efficiently decolorize azo dyes through oxidizing these compounds, which enabled us to develop a method of rapid spectrophotometric determination of persulfate for monitoring the wastewater treatment on the basis of the oxidation decolorization of azo dyes. Four azo dyes with different molecular structures were investigated as probes, and the influences of operation parameters including reaction time, solution pH, initial dye concentration, and initial concentration of activator Fe2+ were checked on the determination of persulfate. Under optimum conditions, the decolorization degree of the dyes responded linearly with persulfate concentration for all the four azo dyes, and the linear range and detection limit were found to be 2.0–150 μmol L−1 and 0.62 μmol L−1 for rhodamine B, 2.0–100 μmol L−1 and 0.42 μmol L−1 for methylene blue, 4.0–150 μmol L−1 and 0.50 μmol L−1 for methyl violet, and 20–150 μmol L−1 and 8.1 μmol L−1 for orange II. A persulfate treatment of a spiked wastewater sample was satisfactorily monitored with the new method.

Optically active polyorthoanisidine, polyorthotoluidine, polyorthoethylaniline and polyorthochloroaniline were synthesized with chemical polymerization of corresponding monomers in aqueous medium by using d- or l-camphorsulfonic acid (d- or l-CSA) as chiral dopant, ammonium persulfate as oxidant, and diaminodiphenylamine as initiator. By circular dichroism spectroscopic measurements, it was found that PANI exhibited generally a reversed chirality in comparison with the used chiral dopant, but the substituted PANIs had the same one as the chiral dopant. This revealed that the substituent at ortho position caused helical inversion of conformation in comparison with the parent PANI. Such effect was further confirmed by the influence of the copolymerization of aniline and its derivatives on the chirality of the copolymers. The effect of the substituent on the chirality of the copolymers was increased with the increase of the steric hindrance of the ortho substituent. A mechanism was proposed to explain the effects of steric hindrance on the chirality of PANIs. The clarified relationship between the steric hindrance and the chirality of the polymer can enable us to tailor the chiroptical properties of functional polymer materials for future application.

Composite films of TiO2 and carbon nanotubes (CNTs) were prepared on titanium sheets by liquid phase deposition and the photoelectrocatalytic (PEC) properties of the films were investigated through the degradation of methyl orange (MO) in 0.1 M solutions. It was demonstrated that CNTs in the TiO2 film significantly decreased the charge transfer resistance and increased the anodic photocurrent response of the film under UV light irradiation when the bias was above −0.1 V. The PEC performance of the CNT-based composite film could be tuned by controlling the preparation parameters including the deposition time and calcination temperature. The deposition time and calcination temperature were optimized at 1 h and 450 °C, respectively. On the TiO2/CNT film prepared under the optimized conditions, 95% of the added MO (10 mg L−1) was degraded within 90 min, which was much higher than the 60% removal seen on the pure TiO2 films.

BiFeO3 magnetic nanoparticles (BFO MNPs) were prepared with a sol−gel method and characterized as a catalyst. It was found that BFO MNPs effectively catalyzed the decomposition of H2O2 into •OH radicals, being confirmed with electron spin resonance spin-trapping technique and other radical probing techniques. The strong H2O2-activating ability of BFO MNPs showed promising applications in the oxidative degradation of organic pollutants. When BFO MNPs were used as a heterogeneous Fenton-like catalyst to degrade Rhodamine B, the apparent rate constant for the RhB degradation at 25 °C at pH 5.0 in the BFO MNPs-H2O2 system was evaluated to be 2.89 × 10−2 min−1, being about 20 folds of that obtained with Fe3O4 MNPs as the catalyst under similar conditions. Moreover, BFO MNPs were demonstrated to have excellent stability and reusability. The catalytic mechanism of BFO MNPs was also investigated with Monte Carlo simulations and density functional theory calculations.

Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) with much improved peroxidase-like activity were successfully prepared through an advanced reverse co-precipitation method under the assistance of ultrasound irradiation. The characterizations with XRD, BET and SEM indicated that the ultrasound irradiation in the preparation induced the production of Fe3O4 MNPs possessing smaller particle sizes (16.5 nm), greater BET surface area (82.5 m2 g−1) and much higher dispersibility in water. The particle sizes, BET surface area, chemical composition and then catalytic property of the Fe3O4 MNPs could be tailored by adjusting the initial concentration of ammonia water and the molar ratio of Fe2+/Fe3+ during the preparation process. The H2O2-activating ability of Fe3O4 MNPs was evaluated by using Rhodamine B (RhB) as a model compound of organic pollutants to be degraded. At pH 5.4 and temperature 40 °C, the sonochemically synthesized Fe3O4 MNPs were observed to be able to activate H2O2 and remove ca. 90% of RhB (0.02 mmol L−1) in 60 min with a apparent rate constant of 0.034 min−1 for the RhB degradation, being 12.6 folds of that (0.0027 min−1) over the Fe3O4 MNPs prepared via a conventional reverse co-precipitation method. The mechanisms of the peroxidase-like catalysis with Fe3O4 MNPs were discussed to develop more efficient novel catalysts.

Sono-enhanced degradation of a dye pollutant Rhodamine B (RhB) was investigated by using H2O2 as a green oxidant and Fe3O4 magnetic nanoparticles (MNPs) as a peroxidase mimetic. It was found that Fe3O4 MNPs could catalyze the break of H2O2 to remove RhB in a wide pH range from 3.0 to 9.0 and its peroxidase-like activity was significantly enhanced by the ultrasound irradiation. At pH 5.0 and temperature 55 °C, the ultrasound-assisted H2O2–Fe3O4 catalysis removed about 95% of RhB (0.02 mmol L−1) in 15 min with a apparent rate constant of 0.15 min−1 for the degradation of RhB, being 6.5 and 37.6 folds of that in the simple catalytic H2O2–Fe3O4 system, and the simple ultrasonic US-H2O2 systems, respectively. The beneficial synergistic behavior between Fe3O4 catalysis and ultrasonic was demonstrated to be dependent on Fe3O4 dosage, H2O2 concentration, pH value and temperature. As a tentative explanation, the observed significant synergistic effects was attributed to the positive interaction between cavitation effect accelerating the catalytic breakdown of H2O2 over Fe3O4 nanoparticles, and the function of Fe3O4 MNPs providing more nucleation sites for the cavitation inception.

A simple and highly sensitive fluorometric method is proposed for the determination of H2O2 in milk samples. In this method, non-fluorescent coumarin is oxidised to highly fluorescent 7-hydroxycoumarin by hydroxyl radicals (OH) generated in a Fenton reaction, and the oxidation product has strong fluorescence with a maximum intensity at 456 nm and can be used as a fluorescence probe for H2O2. Under the optimal conditions (2.5 × 10−4 mol L−1 iron(II) ions, 4.0 × 10−4 mol L−1 coumarin, solution pH 3.0, reaction time 9 min, and excitation at 346 nm), the proposed method presents wide linear responses between the fluorescence intensity and H2O2 concentration in a wide range from 2.0 × 10−8 to 2.0 × 10−5 mol L−1, with a detection limit (S/N = 3) of 5.0 × 10−9 mol L−1. After possible interferences are evaluated for a series of chemical substances, the present method has been applied to the determination of hydrogen peroxide in milk with satisfactory results.

An inorganic molecular imprinted polymer (IMIP) coated photocatalyst for photodegradation of diethyl phthalate (DEP) was synthesized by coating a layer of molecular imprinted silica/alumina on the surface of TiO2nanoparticles with DEP as the template. The characterization with HR-TEM, XRD, FT-IR and UV-visible spectroscopic analysis indicated that the new catalyst was a composite of the TiO2 particle core and a shell layer of Al3+-doped silica with thickness of about 5 nm. The 27Al MAS NMR measurements revealed that the IMIP layer consisted of framework tetrahedrally coordinated aluminium and non-framework octa-coordinated aluminium species, both of which function as the hot spots for the adsorption of target molecules on the catalyst during photocatalysis. It was found that the IMIP layer provided the photocatalyst with molecular recognition ability, leading to selective adsorption and rapid mineralization of the target pollutant from its low level solution (2 mg L−1) in the presence of other high level non-target pollutants, such as phenol (50 mg L−1). Unlike the neat TiO2 photocatalyst (Degussa P25), the use of the IMIP-coated TiO2 photocatalyst almost eliminated the generation of toxic aromatic byproducts. Moreover, the new photocatalyst was totally constructed by inorganic compounds, being resistant to photochemical attack and showing favorable lifetime during the photocatalysis.

Pentachlorophenol (PCP) is a typical highly-toxic pollutant, and its direct photolysis and conventional photocatalysis may produce more toxic by-products such as dibenzodioxins. It is urgently needed to develop a photocatalytic process able to remove PCP without the generation of highly toxic by-products. To achieve this, enzyme-like molecular-imprinted photocatalysts were prepared by using structural analogues of PCP as pseudo templates. It was found that 2,4-dinitrophenol (DNP) was the best template among the tested analogues. The molecular imprinted polymer (MIP) coated P25 TiO2 photocatalyst DNP–P25 prepared with DNP as the template greatly accelerated the photocatalytic degradation of PCP and depressed the generation of toxic intermediates. It was confirmed that the amino groups at the footprint cavities provided a well-defined micro reaction environment, which made the benzene ring of the adsorbed PCP be better exposed to photo-generated reactive OH radicals, leading to easier cleavage of the benzene ring. Both the intermediate analysis and toxicity evaluation confirmed that the MIP-coated TiO2 can make the photocatalytic degradation a safe and green approach of removing PCP.

Molecular imprinted thin films (MIFs) of TiO2 were prepared with a liquid phase deposition (LPD) method, and characterized by FT-IR spectroscopy, UV-visible solid-state reflection spectroscopy, X-ray diffraction, and scanning electron microscopy. Among different approaches of removing the template in the preparation of MIFs, a calcination treatment was the best to produce more 3D “molecular footprint” cavities of the template on the MIF, which promoted further the photocatalytic activity of the MIF in comparison with the films pre-treated by extraction or photodegradation. Compared with the non-imprinted TiO2 film (NIF), the MIF enhanced the photodegradation of the target pollutants by increasing the adsorption of the target pollutants on the surface of the MIF. From the Langmuir–Hinshelwood model, the value of the apparent reaction rate constant on the MIF was obtained, which was much larger than that on the NIF. The equilibrium adsorption constant on the MIF was more than 7 times that on the NIF. Because of this high affinity, the MIF exhibited special molecular recognition ability, leading to selective adsorption and photodegradation of the target pollutant. Moreover, the MIF was confirmed to have good stability during long-time photocatalysis.

Photocatalytic reduction/oxidation and deactivation of TiO2 photocatalyst was investigated in the systems composed of Cr(VI) and salicylic acid. The selection of analysis method of Cr(IV) was very important to the monitoring of the photocatalytic process. It was found that as previously reported, serious deactivation of TiO2 catalyst in the simultaneous photo-reduction of Cr(VI) and oxidation of salicylic acid was incorrectly observed if the Cr(VI) level was analyzed by directly monitoring the absorbance at characteristic 348 nm band of Cr(VI), because it seriously suffers from the interferences of the intermediates generated from the degradation of salicylic acid. By using an appropriate method to determine the Cr(VI) concentration, it was observed that all the added Cr(VI) could be reduced, not showing marked deactivation of the photocatalyst. A long time photocatalytic reduction of Cr(VI) under UV illumination induced the deposition of Cr(III) species on the surface of TiO2 particles, which could cause a mild deactivation of the photocatalyst. However, the accompanied oxidation of salicylic acid was demonstrated to depress the deactivation effect of the deposited Cr(III) species on the photocatalytic activity of the TiO2 photocatalyst.

As a mimetic peroxidase, Fe3O4 magnetic nanoparticles (MNPs) were prepared and used for the determination of hydrogen peroxide (H2O2) based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine sulfate (DPD). Fe3O4 MNPs were found to be able to activate H2O2 and oxidize DPD to a colored product with a strong absorption maximum at 550 nm. Under optimized conditions, the absorbance of the product responded linearly to H2O2 concentration in the range from 0.5 to 150 × 10−6 mol L−1 H2O2 with a detection limit as low as 2.5 × 10−7 mol L−1. The method was successfully applied to the determination of H2O2 in rainwater, honey and milk samples.

Electroactive TiO2 films were prepared by liquid-phase deposition (LPD) in the presence of sodium dodecylsulfonate. The doping of dodecylsulfonate (DS) converted the TiO2 film from a structure of globular nanoparticles to a structure of nano-flakes, which directly influenced the electrochemical behavior of the film. The DS-doped TiO2 film yields an enhanced reduction peak in the cyclic voltammograms, being attributed to the reduction of hydroxylated titanium(IV) species. The varied surface structure of the DS-doped TiO2 film provided a biocompatible platform for immobilizing hemoglobin (Hb), and the Hb-immobilized film electrode exhibited good electrocatalytic activity to the reduction of H2O2. As a sensor for the determination of H2O2, the Hb-immobilized film electrode yielded an excellently linear range from 0.003 to 1.5 mM H2O2 in the correlation between reduction peak current and H2O2 concentration, with a low detection limit of 1.0 μM.

Self-cleaning materials are widely applied, but the available methods for determining their photocatalytic activity are time consuming. A simple analysis method was proposed to evaluate rapidly the photocatalytic activity of self-cleaning materials. This method is based on monitoring of a highly fluorescent product generated by the self-cleaning materials after illumination. Under UV irradiation, holes photo-induced on the surface of self-cleaning materials can oxidize water molecules (or hydroxide ions) adsorbed on the surface to produce hydroxyl radicals, which then quantitatively oxidize coumarin to highly fluorescent 7-hydroxycoumarin. It was observed that the fluorescence intensity of photo-generated 7-hydroxycoumarin at 456 nm (excited at 346 nm) linearly increased with irradiation time, and the fluorescence intensity at a given irradiation time was linearly proportional to the photocatalytic activity of self-cleaning materials. Consequently, the photocatalytic activity of self-cleaning materials was able to be probed simply by using this new method, which requires an analysis time of 40 min, being much less than 250 min required for a dye method.

Very severe reaction conditions are required in the conventional synthesis of molecularly imprinted polymers (MIPs), which is unfavorable to their applications in chemical separation and analysis. A simple surface molecular imprinting approach was developed to synthesize MIP-coated SiO2 micro-particles in aqueous solutions. The 1H NMR and UV–vis spectroscopic analysis indicated that via hydrogen bonding, the functional monomer (o-phenylenediamine) can associate with the target (template) 2,4-dinitrophenol (2,4-DNP), as a model compound of organic pollutants, to form a precursor in aqueous solution. The copolymerization of this precursor and the free monomer was performed in the aqueous suspension of surface modified SiO2 particles, leading to the formation of MIP-coated SiO2 micro-particles. The MIP-coated silica particles were characterized with FT-IR, TGA, and UV–vis solid-state reflection spectroscopy, and were further demonstrated to have high adsorption capacity, excellent selectivity and site accessibility for 2,4-DNP. The new absorbent was successfully used in solid-phase extraction (SPE) to selectively enrich and determine 2,4-DNP in aqueous samples. The experimental results indicated that the MIP-SPE column yielded recoveries higher than 92% with R.S.D. <2.8%, much better than the commercial C18-SPE column, which produced a recovery less than 30% with R.S.D. <3.0%.

In this study, a sensitive and rapid method for hydrogen peroxide (H2O2) determination has been developed with the aid of oxidation decolorization of methyl orange (MO) by using Fenton reactions, because the decolorization extent of MO solution (at the maximum absorption wavelength of 507 nm) is proportion to the concentration of H2O2. Under optimum conditions, this spectrophotometric method for the H2O2 analysis yields a dynamic range of H2O2 concentration from 5.0 × 10−7 to 1.0 × 10−4 mol L−1 (r = 0.997) and a detection limit (3σ/k) of 2.0 × 10−7 mol L−1. This method for the determination of H2O2 (0.04 mmol L−1) is able to tolerate the interference from NaCl (0–5.0 mmol L−1), Na2SO4 (0–5.0 mmol L−1), MgCl2 (0–5.0 mmol L−1), sodium humate (0–0.1 mmol L−1), benzene (0–0.2 mmol L−1), toluene (0–0.2 mmol L−1), chlorobenzene (0–0.2 mmol L−1) and chloroform (0–0.2 mmol L−1). The analysis results for practical rainwater samples are in good agreement with the classical N,N-diethyl-p-phenylenediamine (DPD) method for H2O2 determination.

Poor selectivity of titania (TiO2) photocatalysis is unfavorable to photocatalytic removal of highly toxic low-level organic pollutants in polluted waters in the presence of other less toxic high-level pollutants. A new strategy of increasing this selectivity is the surface modification of TiO2 via coating a thin layer of molecular imprinted polymer (MIP), which provides molecular recognition ability toward the template molecules. By using 2-nitrophenol and 4-nitrophenol as target pollutants, MIP-coated TiO2 photocatalysts were prepared via surface molecular imprinting and were observed to have high activity and selectivity toward the photodegradation of the targets. In the presence of bisphenol A (50 mg L−1) as a nontarget pollutant, the apparent rate constant for the photodegradation of the target 2-nitrophenol and 4-nitrophenol (1.8 mg L−1) over the corresponding MIP-coated TiO2 was 10.73 × 10−3 and 7.06 × 10−3 min−1, being 2.46 and 4.61 times of that (4.36 × 10−3 and 1.53 × 10−3 min−1) over neat TiO2, respectively. The enhanced photocatalytic selectivity was increased when the concentration of the target was decreased and/or when the difference in both the chemical structure and molecule size between the target and nontarget molecules was increased. The increased selectivity was mainly attributed to the special interaction between the target molecules and the footprints polymer via the functional groups (-OH and -NO2).

A simple and reproducible method was developed to synthesize a novel class of Fe3O4/SiO2/dye/SiO2 composite nanoparticles. As promising candidates for use in bioassays, the obtained nanoparticles have an average diameter of 30 nm, and the thickness of the outer shell of silica could be tuned by changing the concentration of the silicon precursor tetraethyl orthosilicate during the synthesis. These multifunctional nanoparticles were found to be highly luminescent, photostable and superparamagnetic. The luminescence intensity of the nanoparticles was increased as the dye concentration was increased in the preparation process. The color of the luminescence was successfully tuned by incorporating different dyes into the nanoparticles. The measurements of the emission spectra indicated that relative to the dye molecules dissolved in ethanol, the emission of the dye-doped nanoparticles exhibited either a red shift or a blue shift, to which a tentative explanation was given.

Photoluminescent dye/polypyrrole nanoparticles were prepared by one-step polymerization of pyrrole monomer in the presence of the dye molecules under UV light illumination. Oxygen in the air was selected as an oxidant in this method. Optical properties of the nanoparticles were investigated, revealing that the nanoparticles exhibited higher photostability than pure RhB. In addition, it was found that the presence of both dye molecules and UV light played the important role in the formation of the nanoparticles. And then the mechanism for the formation of well-confined nanoparticles was explained via the effects of intermolecular energy transfer between the dye molecules and pyrrole monomer on nucleation and growth of polypyrrole.

Trimethoxyborane (B(OMe)3) was confirmed to be an effective precursor for the preparation of spherical boron nitride (BN) particles in the presence of ammonia. The spherical particles with the uniform diameter distribution and smooth surface were synthesized by the chemical vapor deposition (CVD) route, and then novel fluffy-like BN spheres were prepared by using the as-prepared BN ones as CVD substrates. The microscopy and spectroscopy examination indicated that the spheres consist of smooth core and fluffy shell. The second growth induced abundant defects at the surface of the fluffy BN spherical structure, which is important for the novel materials as a catalyst support with high loading amount of metal.

Molecular imprinted polymer coated photocatalysts were prepared via polymerization of a proper functional monomer in the presence of TiO2 nanoparticles and target molecules, which was found to promote the selectivity of TiO2 photocatalysis.

Ultrasonic oxidation of iodide was investigated in the presence of carbon tetrachloride (CCl4). The ultrasonic oxidation of potassium iodide led to formation of iodine and then I3− in the presence of excess iodide, and the generated I3− shows strong UV absorption with a molar absorptivity of 2.31 × 104 L mol−1 cm−1 at the maximum absorption wavelength of 351 nm. The ultrasonic oxidation of iodide was found to be significantly promoted by a small addition of CCl4, and it was further found that the generation rate was increased with the amount of CCl4 added. This can be used to analyze the level of CCl4 dissolved in aqueous solutions. Under optimum conditions, the concentration of generated iodine (or its absorption at 351 nm) was found to correlated linearly with the concentration of CCl4 in the range of 0.2–50 mg L−1 (detection limit = 0.09 mg L−1, R2 = 0.999). As an alternative indirect spectrophotometric method of CCl4 determination, the proposed method was successfully applied to determine the concentrations of CCl4 in several practical samples, showing merits of being sensitive and simple of operation.

A sensitive method for carbon tetrachloride (CCl4) determination has been developed with the aid of ultrasonic oxidation decolorization of methyl orange (MO). It is found that the ultrasonic oxidation decolorization rate of MO can be significantly promoted by adding a little amount of CCl4. The increased ultrasonic decolorization rate of MO is strongly dependent on the concentration of CCl4 added, and a linear correlation is observed between the amount of CCl4 and the decolorization rate of MO in the ultrasonic oxidation process. Thus, the CCl4 determination is transformed to a simple and direct determination of the decoloration extent of MO solution at a given concentration. As an indirect spectrophotometric determination of CCl4, the new method is sensitive and easy of operation with a maximum wavelength of 508 nm, molar absorptivity of 3.83 × 104 L mol−1 cm−1, and a Sandell sensitivity of 7.96 × 10−3 μg cm−2. Under optimized conditions, Beer's law is obeyed in the range of 0.4–20 mg L−1 of CCl4 (DL = 0.19 mg L−1, r = 0.9996). The concentrations of CCl4 in several practical samples have been determined satisfactorily by using this method.

Effects of CCl4 were investigated on the ultrasonic decolorization of azo dye methyl orange (MO). The decolorization of MO was observed to behave as a pseudo-first reaction in kinetics under all the conditions tested in the present work. The apparent rate constant of the decolorization was demonstrated to be dependent on CCl4 concentration, MO concentration and the solution pH value. Under appropriate conditions, the rate constant of the ultrasonic decolorization of MO was able to be increased more than 100 times by adding CCl4 into the MO solution. A reaction mechanism was proposed to explain the promoting effect of CCl4 on the ultrasonic decolorization of MO, which was attributed to the generation of highly-oxidizing such as Cl radical and HClO species, and then their attack at the azo bond of MO.

A peculiar cyclic voltammetric behavior of polyaniline (PANI) film was observed in acetonitrile (ACN) solution. When the potential was scanned in a narrow potential window corresponding to the first conventional redox pair for the conversion between leucoemeraldine and emeraldine in ACN solution, splitting of the anodic peak for the oxidation from leucoemeraldine to emeraldine was observed in the cyclic voltammograms. When the low limit of the potential window was shifted to a potential negative enough, the cyclic voltammograms of PANI changed significantly, and the electrical properties of PANI film also changed due to the treatment. These peculiar behaviors were tentatively suggested to be associated with the deep reduction, accompanied by the structural changes of PANI chains due to the dedoping. It was further found that when the PANI film was treated by pre-cycling in potential windows with low limits more negative than −0.8 V, its sensitivity was significantly increased toward ammonia vapor, being little affected by the humidity. This led to a successful fabrication of a concept ammonia sensor by using the PANI film pretreated by the deep reduction.

Photocatalytic degradation of colorless aniline and phenolic pollutants was investigated over TiO2 under visible-light irradiation, which was confirmed to proceed via a charge-transfer-complex (CTC)-mediated pathway. The correlation between the chemical structure and the degradation rate of these pollutants was established experimentally and theoretically. It was found that an electron-donating substituent in benzene ring, which raises the highest occupied molecular orbital and lowers the ionization potential of the organic compound, is favorable to the CTC-mediated photodegradation of the pollutant, but an electron- withdrawing substituent has a reversed effect. The addition of sacrificial electron acceptors was adopted to enhance the degradation and mineralization of the aromatic pollutants. The increased degradation rate by 3 to 10 times suggests that the CTC-mediated photocatalytic technique has promising applications in the removal of colorless organic pollutants in the presence of sacrificial electron acceptors.Charge transfer complexes enhance the photo catalytic activity of titania for degradation of organic pollutants under visible light.Download high-res image (21KB)Download full-size image

Persulfate can efficiently decolorize azo dyes through oxidizing these compounds, which enabled us to develop a method of rapid spectrophotometric determination of persulfate for monitoring the wastewater treatment on the basis of the oxidation decolorization of azo dyes. Four azo dyes with different molecular structures were investigated as probes, and the influences of operation parameters including reaction time, solution pH, initial dye concentration, and initial concentration of activator Fe2+ were checked on the determination of persulfate. Under optimum conditions, the decolorization degree of the dyes responded linearly with persulfate concentration for all the four azo dyes, and the linear range and detection limit were found to be 2.0–150 μmol L−1 and 0.62 μmol L−1 for rhodamine B, 2.0–100 μmol L−1 and 0.42 μmol L−1 for methylene blue, 4.0–150 μmol L−1 and 0.50 μmol L−1 for methyl violet, and 20–150 μmol L−1 and 8.1 μmol L−1 for orange II. A persulfate treatment of a spiked wastewater sample was satisfactorily monitored with the new method.

The effect of EDTA on the H2O2 activation ability of Fe3O4 nanoparticles was investigated for removing organic pollutants. Regular Fe3O4 nanoparticles were observed to have moderate catalytic activity, which was not suitable for the degradation of various organic pollutants. The addition of EDTA enhanced the activation of H2O2 on the surface of Fe3O4 nanoparticles, thereby accelerating the formation of reactive oxygen species and increasing the degradation rates of pentachlorophenol, sulfamonomethoxine, and Rhodamine B by 84.4, 48.3, and 17.5 times, respectively, at pH 5.0 and 40 °C. Based on spectroscopic and density functional theory studies, adsorption mechanisms for H2O2 and EDTA on the surface of Fe3O4 nanoparticles were proposed. It was clarified that the enhancing effect of EDTA was attributed to an appreciable improvement of Fe3+/Fe2+ recycling on the surface of Fe3O4 nanoparticles, and to the simultaneous degradation of EDTA and target pollutants.

Molecular imprinting technology allows synthesis of polymers with specific recognition ability towards target pollutants, which show potential to selectively remove Highly Toxic Organic Pollutants (HTOPs) in the presence of common organic matrices that are thousands of times more abundant than the targets. This feature article summarizes the current development of molecular imprinting for removing HTOPs from polluted water, with a special emphasis on the application of molecularly imprinted polymers to improve the efficiency of photocatalytic and biological degradation of HTOPs in wastewater.

Molecular imprinted polymer coated photocatalysts were prepared via polymerization of a proper functional monomer in the presence of TiO2 nanoparticles and target molecules, which was found to promote the selectivity of TiO2 photocatalysis.

By using cobalt nitrate and bismuth nitrate as precursor salts and NaOH as a precipitation agent, Co3O4–Bi2O3 nanocomposite oxides (CBO) were prepared as a heterogeneous catalyst for the activation of peroxymonosulfate (PMS) by a conventional reverse co-precipitation method and post-calcination. The characterization with transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and Raman spectroscopy demonstrated that there was a strong interaction between Bi and Co components in CBO. The presence of Bi increased the content of surface hydroxyl oxygen, which favored the formation of Co(II)–OH complexes that were vital for heterogeneous activation of PMS. CBO showed strong catalytic activity in the heterogeneous activation of PMS for degradation of organic pollutants such as methylene blue (MB), rhodamine B, phenol and 2,4-dichlorophenol. With the addition of 0.5 mmol L−1 PMS, CBO produced fast and full degradation of MB (20 μmol L−1) with the apparent rate constant of 0.36 min−1, being 8.6 fold of that (0.042 min−1) over nano-Co3O4. It decreased the cobalt leaching to 43 μg L−1, being much less than that (158 μg L−1) from Co3O4 under the same conditions. The effects of CBO loading, PMS concentration and calcination temperature on the degradation of MB and cobalt leaching were also investigated.

An inorganic molecular imprinted polymer (IMIP) coated photocatalyst for photodegradation of diethyl phthalate (DEP) was synthesized by coating a layer of molecular imprinted silica/alumina on the surface of TiO2nanoparticles with DEP as the template. The characterization with HR-TEM, XRD, FT-IR and UV-visible spectroscopic analysis indicated that the new catalyst was a composite of the TiO2 particle core and a shell layer of Al3+-doped silica with thickness of about 5 nm. The 27Al MAS NMR measurements revealed that the IMIP layer consisted of framework tetrahedrally coordinated aluminium and non-framework octa-coordinated aluminium species, both of which function as the hot spots for the adsorption of target molecules on the catalyst during photocatalysis. It was found that the IMIP layer provided the photocatalyst with molecular recognition ability, leading to selective adsorption and rapid mineralization of the target pollutant from its low level solution (2 mg L−1) in the presence of other high level non-target pollutants, such as phenol (50 mg L−1). Unlike the neat TiO2 photocatalyst (Degussa P25), the use of the IMIP-coated TiO2 photocatalyst almost eliminated the generation of toxic aromatic byproducts. Moreover, the new photocatalyst was totally constructed by inorganic compounds, being resistant to photochemical attack and showing favorable lifetime during the photocatalysis.