Hierarchical citrate modified ferrihydrite microstructures (Fh1) with flower-like morphologies were successfully synthesized via a simple aqueous solution route without the addition of any organic solvent or surfactant. The obtained products were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), BET analyses, Fourier-transform IR spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The prepared citrate modified ferrihydrite microstructures (Fh1) exhibited superior adsorption abilities for removal of methylene blue (MB) and Cr(VI) ions from aqueous solution. In addition, these citrate modified ferrihydrite microstructures also exhibited high activity to produce hydroxyl radicals through catalytic decomposition of H2O2 and could degrade highly concentrated MB solution at neutral pH. The results indicate that citrate modified ferrihydrite microstructures are very promising adsorbents and (photo-) Fenton-like catalysts for the treatment of pollutants.

This paper describes the preparation of lepidocrocites (γ-FeOOH) via the air oxidation of Fe(OH)2 under visible light irradiation in the presence of oxalic acid. Experimental results show that lepidocrocites with different degrees of crystallization can be obtained by controlling the concentration of oxalic acid under visible light irradiation. The crystallization of γ-FeOOH is found to gradually decrease with the increase of oxalic acid concentration. This provides an alternative approach for the synthesis of low-crystalline γ-FeOOH. Based on the results, a possible oxidation mechanism of Fe(II) has been proposed, which involves the formation of an Fe(II)–oxalate complex under light irradiation to produce oxidizing species, leading to an increase of the oxidation rate. The higher oxidation rate favors the formation of low-crystalline γ-FeOOH. In contrast to the high-crystalline γ-FeOOH, the low-crystalline γ-FeOOH with high specific surface shows higher adsorption and photocatalytic activity toward the photodegradation of orange II.

Ferrihydrite (Fh) is a naturally occurring nanoscale iron oxyhydroxide mineral. It is of great interest in soil science and environmental science due to its extremely high surface area and reactivity. In this work, Fh samples were prepared by three procedures (named Fh-1, Fh-2, and Fh-3). The formation of Fh-1 went through a pH change from acidic to neutral, and the formation of Fh-2 went through a pH change from alkaline to neutral, while Fh-3 was formed at a constant neutral pH. The three Fhs were characterized by high-resolution transmission electron microscopy (HRTEM), terahertz (THz) spectroscopy, nitrogen adsorption isotherms, and low-temperature magnetic techniques. All these techniques indicate that the microstructure and formation process of Fh are strongly coupled. More importantly, the differences in microstructure among the three Fhs are reflected not only in their bulk structure but also in their surface properties. The adsorption and degradation of azo dye Mordant Yellow 10 (MY10) on the three Fhs were investigated. On the one hand, compared with Fh-1 and Fh-2, Fh-3 exhibits a high density of active sites per unit area, which leads to a large adsorption capacity. On the other hand, a strong affinity between Fh-3 and MY10 results in a more irreversible adsorption and a low degradation rate. The results from the current study shed new light on the synergetic effects of porosity and the variations of local structure on photocatalysis by iron oxide particles.

In this paper, a simple and efficient route had been developed for morphology-controlled synthesis of hierarchical α-Fe2O3 superstructures assembled by nanocrystallites. All chemicals used were low-cost compounds and environmentally benign. The morphologies and structures of the α-Fe2O3 crystals were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier-transform IR spectroscopy (FTIR). The results showed that different shapes of hierarchical α-Fe2O3 nanostructures such as peanuts-like, capsule-like, cantaloupe-like and almond-shaped could be prepared by simply varying the concentration of silicate anions and other inorganic reagents. The as-prepared α-Fe2O3 architectures were composed of nanorods or nanosheets at different synthesis temperature. The possible formation mechanism was described based on the experimental results. Magnetic hysteresis measurements revealed the as-prepared superstructures displayed ferromagnetic behavior with higher remanence and coercivity at room temperature, which was attributed to the superstructure or the shape anisotropy of the samples.Highlights► Hematite nanostructures were prepared though template-free hydrothermal reaction. ► All chemicals used were low-cost compounds and environmentally benign. ► The shapes of hematite nanostructures could be well controlled. ► The building blocks of hematite were finely controlled by varying temperature. ► The as-prepared superstructures display higher remanent magnetization and coercivity.

The heterogeneous catalytic reaction of H2O2 with iron oxides is an important reaction for the environment since both H2O2 and iron oxides are common constituents of natural and atmospheric waters. In this work, three ferrihydrites, labeled Fh-1, -2 and -3, were prepared by different procedures. Fh-1 was prepared by adding alkali solution to ferric solution under stirring. In the preparation of Fh-2, the mixing procedure of the two solutions was reversed. Fh-3 was obtained by adding alkali solution and ferric solution simultaneously into a certain amount of water. The heterogeneous catalytic reaction of H2O2 with three ferrihydrites in aqueous solution was investigated in detail. The results demonstrated that the apparent reaction rate was affected by the preparation procedure of ferrihydrite besides pH, temperature and the dose of catalyst. The activation energy of the decomposition reaction of H2O2 was determined to be 76.13, 59.41 and 68.05 kJ mol−1 for Fh-1, -2 and -3, respectively. The activation enthalpy of the reaction were determined to be 73.59, 56.56 and 65.76 kJ mol-1 and the activation entropy of the reaction were determined to be −69.65, −119.67 and −90.58 J mol−1 K−1, respectively.Graphical AbstractThis research supplies a new insight on the decomposition kinetics of hydrogen peroxide catalyzed by ferrihydrites prepared using three procedures.Highlights► Ferrihydrite (Fh) was prepared using three different procedures. ► Rate of catalytic decomposition H2O2 on the three Fhs is different. ► Activation energy, activation enthalpy and activation entropy of the reaction were calculated.

Lepidocrocite was synthesized by aerial oxidation using an FeIIEDTA solution. The synthesis was performed under irradiation from different monowavelength light emitting diode (LED) lamps at room temperature. X-ray diffraction results showed the formation of differently crystallized lepidocrocite. The indirect bandgap values of the lepidocrocite samples were about 2.34, 2.36, and 2.31 eV for red, green, and blue light, respectively. The kinetics of the photo-decolorization of crystal violet (CV) was investigated in a system composed of lepidocrocite, H2O2, and visible light. H2O2 concentration, light irradiation, and catalyst concentration were also investigated. The rate of CV decolorization was found to fit pseudo-first-order kinetics. The results show that different as-prepared lepidocrocite have different adsorption and photocatalytic characteristics. A possible mechanism was also suggested for the dye degradation.Graphical abstractLepidocrocite with different indirect bandgap values was synthesized by aerial oxidation FeIIEDTA solution under different monowavelength LED lamps irradiation at room temperature. Different photocatalytic activity was found in the decolorization of crystal violet dye.Highlights► Lepidocrocite was room-temperature synthesized by monowavelength LED irradiation. ► Different wavelength irradiation led to different Eg value of lepidocrocite. ► γ-FeOOH obtained by blue LED irradiation has the highest Γmax and catalytic activity. ► A mechanism was suggested for the degradation of crystal violet dye.

A novel microemulsion method is described for the in situ synthesis of α-Fe2O3 nanoparticles with ferrihydrite as a precursor and trace Fe (II) as a catalyst. The final products are characterized by XRD and TEM techniques. The influence of various factors on the transformation from ferrihydrite to hematite nanoparticles is investigated. The effects of ω (ω = nH2O / nCTAB) and weight ratio of CTAB to n-octane on the size of α-Fe2O3 nanoparticles are also studied, respectively.A novel microemulsion method is described for the in situ synthesis of α-Fe2O3 nanoparticles with ferrihydrite as a precursor and trace Fe (II) as a catalyst which does not require any calcination step. The nanoparticles were characterized by X-ray diffractometer (XRD) and transmission electron microscopy (TEM). It was found that the size of α-Fe2O3 nanoparticles was influenced by ω (ω = nH2O / nCTAB) and weight ratio of CTAB to n-octane.

The mechanism of formation of hematite particles in the Fe-HNO3 system is investigated by introduction of a small amount of PO43− ions to the system. The intermediate species in the reaction, 6-line ferrihydrite, is successfully obtained. The transformation of 6-line ferrihydrite to hematite is investigated. The results show that Fe(II) in the Fe-HNO3 system can catalyze the dissolution of 6-line ferrihydrite, leading to the rapid formation of hematite.Graphical abstractHighlights► 6-Line ferrihydrite was an important intermediate species in the Fe-HNO3 system. ► Fe(II) ions can catalyze the transformation of 6-line ferrihydrite to hematite. ► Hematite was obtained by the dissolution–recrystallization of 6-line ferrihydrite.

We have investigated the catalytic transformation of ferrihydrite, feroxyhyte, and lepidocrocite in the presence of Fe(II). In this paper, the transformation from akaganeite and goethite to hematite in the presence of trace Fe(II) was studied in detail. The result indicates that trace Fe(II) can accelerate the transformation of akaganeite and goethite. Compared with the transformation of other iron oxyhydroxides (e.g., ferrihydrite, feroxyhyte, lepidocrocite, and akaganeite), a complete transformation from goethite to hematite was not observed in the presence of Fe(II). On the basis of our earlier and present experimental results, the transformation of various iron oxyhydroxides was compared based on their thermodynamic stability, crystalline structure, transformation mechanism, and transformation time.Graphical abstractThe transformation of various iron oxyhydroxides in the presence of trace Fe(II) was compared based on experimental results, thermodynamic stability, crystalline structure, and transformation mechanism .Highlights► Fe(II) can accelerate the transformation from akaganeite to hematite. ► Small particles of goethite can transform to hematite in the presence of Fe(II). ► Some hematite particles were found to be embedded within the crystal of goethite. ► The relationship between structure and transformation mechanism was revealed.

This work examined Fe(II)-induced transformation of ferrihydrite in the presence of ammonia, amine and the coordination ions of Fe(III). Our earlier results showed that ferrihydrite transformed into the mixture of lepidocrocite, goethite and/or hematite in the presence of trace Fe(II) and absence of ammonia and similar species. However, the formation of lepidocrocite was restrained when using ammonia as precipitants. When introducing some amines (e.g. ethanolamine and diethanolamine) and some coordination ions (e.g. F− and C2O42− ions) into the reaction system, a similar effect on the transformation of ferrihydrite was found. Probably, the complexes formed between Fe(III) and those additives favor the formation of goethite. At the same time, the introduction of these additives hinders Fe(II) from interacting with ferrihydrite, which makes the catalytic dissolution of ferrihydrite be limited, thus, the formation of lepidocrocite be restrained.Fe(II)-induced transformation of ferrihydrite in the presence of ammonia, amine and coordination ions of Fe(III) was studied. The introduction of the additives favors the formation of goethite.

A rational new method for the synthesis of variable-sized Fe3O4 nanoparticles by aerial oxidation of Fe(OH)2 under visible light irradiation in the presence of trace EDTA has been investigated. The size of the Fe3O4 nanocrystals was controlled at about 11.5−30.0 nm by varying the reaction conditions in aqueous solution at room temperature. The oxidation reaction was significantly accelerated by visible light in the presence of EDTA. A rapid oxidation rate was favorable for decreasing the size of the Fe3O4 nanocrystals. The as-obtained Fe3O4 particles showed uniform spherical shape and a narrow size distribution. The variable-sized Fe3O4 nanocrystals exhibited different magnetic properties.

Using a combination of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, we have studied the growth of ZnO nanowhiskers using a simple solution synthetic process. We find that the formation of ZnO nanowhiskers involves simultaneous nucleation of Zn(OH)2 and ZnO in the same solution, the subsequent competing growth of octahedral-shaped ε-Zn(OH)2 and flower-like ZnO crystals in the early stages which results in a stable intermediate product ε-Zn(OH)2 microcrystals, and then a phase transformation from ε-Zn(OH)2 to ZnO nanowhiskers which follows the in situ crystallization mechanism in the later growth. The existence of the stable ε-Zn(OH)2 microcrystals is a necessary condition for the growth of one-dimensional (1D) ZnO nanowhiskers in this process. The temperature and basicity of the reaction solution play important roles in the competing growth of ε-Zn(OH)2 and flower-like ZnO, that is, low temperature and low basicity facilitate the nucleation and growth of ε-Zn(OH)2.

Anatase TiO2 powders with high thermal stability and specific surface area were successfully prepared by an alcohothermal method, using tetra-n-butyl titanate [Ti(OC4H9n)4] as a precursor. Even calcination at 800 °C for 4 h, the X-ray diffraction (XRD) pattern of the obtained TiO2 showed that the main crystal phase was still anatase. The specific surface area of the TiO2 calcined at 200 °C was 219.5 m2·g− 1, and that of the samples calcined at 800 °C still maintained 102.9 m2·g− 1 with narrow pore-size distribution (2.0–10.0 nm). High magnification transmission electron microscopy (TEM), fourier transformation infrared (FT-IR) spectra and thermo-gravimetric analysis (TGA) and simultaneous differential thermal analysis (SDTA) indicated that alcohothermal method was favorable for the formation of the very small TiO2 particles and TiOC4H9 groups on the surface of TiO2, which were regarded as key effects to increase the thermal stability of anatase TiO2.Anatase TiO2 powders with high thermal stability and specific surface area were successfully prepared by an alcohothermal method. Even calcination at 800 °C for 4 h, the main crystal phase of the obtained TiO2 was still anatase, and the specific surface area maintained 102.9 m2·g− 1 with narrow pore-size distribution (2.0–10.0 nm).

Two-line ferrihydrite was prepared by two different procedures. In procedure 1, which is widely used, ferrihydrite (named as ferrihydrite-1) was prepared by droping NaOH solution into Fe(III) solution. In procedure 2, which is rarely reported, ferrihydrite (named as ferrihydrite-2) was prepared by adding Fe(III) and NaOH solutions into a certain volume of water simultaneously. The results showed that mixing procedures of Fe(III) and alkaline were critical in the sub-microstructures and the conversion mechanisms of ferrihydrites in the presence or absence of trace Fe(II). The sub-microstructure of ferrihydrite-1 favored the mechanism of its dissolution re-crystallization and hematite nanoparticles with rough surface were obtained. The sub-microstructure of ferrihydrite-2 favored the solid state transformation from ferrihydrite to hematite and hematite nanoparticles with smooth surface were formed. These research results will be helpful for us to control the synthesis of hematite nanoparticles with different surface state.Ferrihydrites prepared by mixing Fe3+ and NaOH solutions according to different procedures can rapidly transform into hematite particles with different surface structures in the presence of trace Fe(II).

δ-FeOOH, a poorly crystalline iron oxyhydroxide, can transform to the more stable iron oxyhydroxide or oxide. In the present work, the transformation from δ-FeOOH to goethite and hematite in the presence of trace Fe(II) has been investigated. The results show that Fe(II) can catalyze this transformation of δ-FeOOH. Based on experimental results and literature data, it is confirmed that two transformation mechanisms exist in the current system. One is the catalytic dissolution of δ-FeOOH, which leads to the formation of both hematite and goethite. The other is the catalytic solid-state transformation from δ-FeOOH to hematite. Which mechanism predominates depends on the temperature, pH, heating rate, etc. The results reveal that high temperatures (in the range from room temperature (RT) to 100 °C) favor the solid-state transformation as well as the formation of hematite. Given the structural relationships observed between δ-FeOOH and hematite, it is possible that the solid-state transformation from δ-FeOOH to hematite can exist.

The inhibitory effect of phosphate on the crystal grain growth of nanosized titania during high temperature calcination was investigated. Nanosized titanium dioxide powders prepared by hydrolysis of titanium tetrachloride were soaked in phosphate solutions with different concentrations. The obtained powders calcined at various temperatures were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectronic spectroscopy (XPS). The grain size of the samples without phosphate treatment increased quickly when calcined at high temperatures, while the grain size of the samples with phosphate modification increased slowly when calcined at the same temperature. This phenomenon implies that phosphate treatment plays an important role in inhibiting the crystal grain growth of titania. The possible mechanism of the inhibition effect of phosphate on titania is discussed.

One-dimensional (1D) needle-like ZnO nanowhiskers have been grown directly from aqueous solution containing Zn(OH)42− ions which is produced by zinc chloride and sodium hydroxide, in the presence of sodium dodecyl sulfate (SDS). Through the improved novel approach, uniform ZnO nanowhiskers with diameters ranging from 80 to 120 nm and an average length of about 4 μm (aspect ratio ∼40:1) were successfully prepared at a low hydrothermal temperature (85 °C) with a short reaction time (5 h). The nanowhiskers exhibit a perfect single crystalline wurtzite structure with [0 0 0 1] as the growth orientation. The growth mechanism, as well as the controllable factors on the crystal size and shape, is also discussed in detail.

The transformation from ferrihydrite to various iron oxides and iron oxyhydroxides has been given much attention not only in environmental science and geochemistry but also in biology and material science. This laboratory study attempted to investigate Fe(II)-induced transformation of ferrihydrite in sulfate-rich medium. The results indicate that the transformation in sulfate-rich medium differs from that in Cl− medium in the species, the amount and the morphology of products and transformation rate. Lepidocrocite is a main ingredient in the product in Cl− medium at room temperature (RT), while goethite is the only product in SO42− medium at RT. Goethite particles obtained in Cl− medium are star-like but rod-like in SO42− medium. The transformation rate in the latter medium is obviously slower than that in the former medium. The formation of lepidocrocite depends on both the ionic strength of the system and the dissolution rate of ferrihydrite.Fe(II)-induced transformation of ferrihydrite in sulfate-rich medium was studied. Lepidocrocite is a main ingredient in the product in Cl− medium at room temperature (RT), while goethite is the only product in SO42− medium. Goethite particles obtained in Cl− medium are star-like but rod-like in SO42− medium.

Well-defined flower-like ZnO microstructures with different sizes and shapes have been successfully synthesized via a simple aqueous solution route, using zinc chloride and sodium hydroxide as the reactants, triethanolamine (TEA) as the modifying agent. The XRD pattern indicated that the obtained ZnO microcrystals were of wurtzite structure. SEM and TEM images illustrated that the flower-like ZnO bundles consisted of some prism-like or petal-like branches, which can be further characterized as single crystals in nature and preferentially growing up along [0 0 0 1] by SAED and HRTEM studies. The solution basicity has determinative effects on the morphology, size, as well as dimensionality of the obtained ZnO microcrystals by mediating the nucleation and crystal growth rate. Furthermore, the uneven adsorption of TEA on (0 0 0 1) plane of the growing ZnO crystal leads to the tapering feature of the branches, which resemble vividly the flower petals in appearance.

Spherical hematite particles have been quickly synthesized by heating Fe(OH)3 gel with trace Fe(II) in aqueous solution to reflux temperature. The final product is characterized by XRD, TEM, HRTEM, and FT-IR techniques. The influence of various factors on the size and morphology of hematite particles is investigated, respectively. The growth mechanism of hematite particles is also discussed. The results show that both the mechanisms, dissolution/reprecipitation and solid state transformation, work alternately in the transformation process from Fe(OH)3 to hematite particles until the transformation is finished. The magnetism of the product is also studied.

The transformation of Fe(II)-adsorbed ferrihydrite was studied. Data tracking the formation of products as a function of pH, temperature and time is presented. The results indicate that trace of Fe(II) adsorbed on ferrihydrite can accelerate its transformation obviously. The products are lepidocrocite and/or goethite and/or hematite, which is different from those without Fe(II). That is, Fe(II) not only accelerates the transformation of ferrihydrite but also leads to the formation of lepidocrocite by a new path. The behavior of Fe(II) is shown in two aspects—catalytic dissolution–reprecipitation and catalytic solid-state transformation. The results indicate that a high temperature and a high pH(in the range from 5 to 9) are favorable to solid-state transformation and the formation of hematite, while a low temperature and a low pH are favorable to dissolution–reprecipitation mechanism and the formation of lepidocrocite. Special attentions were given to the formation mechanism of lepidocrocite and goethite.Fe(II)-adsorbed ferrihydrite can rapidly transform into lepidocrocite or/and goethite or/and hematite. Which product dominates depends on the transformation conditions of ferrihydrite such as temperature, pH, reaction time, etc. In the current system, there exist two transformation mechanisms. One is dissolution/reprecipitation and the other is solid-state transformation. The transformation mechanisms from Fe(II)-adsorbed ferrihydrite to lepidocrocite and goethite were investigated.

The synthesis of rutile (TiO2) nanostructured materials at low temperature from TiCl4 aqueous solution was described. TiO2 coatings on polystyrene (PS) particles were prepared by layer-by-layer assembly technique. The samples were characterized by DTA-TG, SEM, XPS, TEM and XRD techniques. The experimental results showed that pure rutile-TiO2 coatings with nanocrystal structure were synthesized at 100 °C. On the surface of PS particles, sphere-type TiO2 coatings exhibited uniform shape and a narrow size distribution. The amount of TO2 (wt%) and shell thickness of particles increased with the adding of coating layers. Hollow TiO2 spheres were obtained by calcination at 450 °C. TiO2/PS with 2 coating layers showed higher degradation rate. The photocatalytic activity of hollow TiO2 spheres was higher than that of TiO2/PS.

By heating Zn(OH)2 precursor in aqueous solution to reflux temperature (101 °C), ZnO microparticles with a diversity of well-defined morphologies, including rod-like, nut-like, and rice-like samples, have been successfully synthesized. The shape of the crystallite depends critically on the additive added in the reaction solution. To further understand the effect of the additive on the formation process of ZnO crystallite, scanning electron microscopy analyses of the solid product and concentration measurements of zinc ion remaining in the solution have been made at regular intervals throughout the reaction with and without the addition of sodium dodecyl sulfate (SDS) and triethanolamine (TEA). Results show that SDS and TEA added in the solution remarkably lower the formation rate of ZnO crystallite.ZnO microparticles with a diversity of well-defined morphologies, including rod-like, nut-like, and rice-like samples, were successfully synthesized in aqueous solution. The effects of the additives on the formation process of ZnO crystal were preliminarily revealed.

The objective of the research is to determine the effects of Fe(II) on the phase transformation from ferrihydrite to hematite in pH range 5–9 at 100 °C. It is confirmed that Fe(II) is a catalyst in the process of phase transformation of ferrihydrite. On one hand, Fe(II) can catalyze the formation of hematite by a dissolution/reprecipitation mechanism. On the other hand, Fe(II) can catalyze the formation of hematite by a solid-state transformation. The species of Fe(II) that take catalytic action on the phase transformation of ferrihydrite are probably FeOH+ and Fe(OH)2. Both dissolution/reprecipitation and solid-state transformation can be explained by electron transfer. This phase transformation from ferrihydrite to hematite, which is called as catalytic phase transformation, can be employed to synthesize hematite particles rapidly.Hematite forms rapidly from ferrihydrite in the presence of trace amounts of Fe(II) by two mechanisms.

The phase transformation from Fe(OH)3 gel to α-Fe2O3 particles at different initial pHs at about 100 °C was studied. The time necessary for completing the above process was determined. The results showed that the time of phase transformation from Fe(OH)3 gel to α-Fe2O3 particles shortened with the increase of initial pH at pH < 4.5. In this pH range, β-FeOOH, as an intermediate product, was obtained and hematite was formed by dissolution/reprecipitation mechanism. However, in the pH range from 4.5 to 9.0, the transformation time prolonged with increasing pH. In this pH range, no intermediate product was found. From Fe(OH)3 gel to hematite, there are two transformation pathways. One is the dissolution/reprecipitation mechanism and the other is the solid state transformation mechanism. With the pH close to the point of zero charge (pzc) of Fe(OH)3 gel, the later mechanism gradually predominated.

One-dimensional (1D) needle-like ZnO nanowhiskers have been grown directly from aqueous solution containing Zn(OH)42− ions produced by zinc chloride and sodium hydroxide, in the presence of sodium dodecyl sulfate (SDS).

•Adsorption and degradation of RhB during lepidocrocite formation were analyzed.•Adsorption and degradation of RhB were affected by the action of system itself.•Comprehensive effect occurred in the degradation of RhB during the reaction.This paper described the adsorption and degradation of rhodamine B (RhB) during lepidocrocite (γ-FeOOH) formation by air oxidation of Fe(OH)2 under visible-light irradiation in the presence of trace ethylenediaminetetracetic acid (EDTA). The results showed that RhB could be adsorbed on a green rust II (GR II) intermediate and on the γ-FeOOH product surface during γ-FeOOH formation and be degraded via heterogeneous and homogeneous photo-Fenton-like reactions. Fe2+ and H2O2 coexisted in the reaction system, and Fe2+ or H2O2 both promoted the adsorption and degradation of RhB. As the reaction proceeded, the increase in acidity enhanced the efficiency of the photo-Fenton-like reactions, which led to an increase in RhB degradation. The adsorbed RhB exhibited desorption behaviors because of the transformation of GR II and growth of γ-FeOOH. A possible mechanism was suggested for the comprehensive effect of RhB degradation during the reaction.Download full-size image

•Fhs were prepared using three different procedures.•Three Fhs exhibit different sorption capacity and affinity for Cu(II) ions.•The experimental data were well fitted by double layer surface complexation model.Binding ability of heavy metal ions on the surface of environmental minerals may greatly affect the local chemical properties, long-range interactions, surface reactivity, and bioavailability of metal ions in the aquatic environment. In this work, three ferrihydrites (Fh-1, Fh-2 and Fh-3) were prepared by different clearly defined procedures. Among them, the formation condition of Fh-3 is close to that of ferrihydrite in natural environment. The adsorption characteristics of the Cu(II) ions on the three ferrihydrites were investigated. The affinity of three ferrihydrites to Cu(II) ions was evaluated based on pH-sorption edge curves, Langmuir and Freundlich model parameters, adsorption–desorption isotherms and ageing of ferrihydrite adsorbed Cu(II). The results indicate that the maximum adsorption capacity for Cu(II) was found to be 8.74, 13.33 and 14.39 mg g−1 for Fh-1, Fh-2 and Fh-3, respectively. Fh-2 and Fh-3 have stronger affinity than Fh-1 to adsorb Cu(II) ions. The experimental data were well fitted by double layer surface complexation model. The sorption differences of Cu(II) on the three Fhs were investigated by results gained from the simulation.Ferrihydrites prepared by three procedures exhibit different adsorption capacity and affinity for Cu(II) ions.Download full-size image

•A series of jarosite-type compounds was prepared.•The as-prepared samples exhibit a novel trigonal antiprismatic shape.•The formation mechanism of trigonal antiprismatic jarosite-type compounds was investigated.Trigonal antiprismatic jarosite-type compounds were prepared by a simple, rapid and template-free synthetic route. The as-prepared samples were characterized by various techniques. The results indicate that the formation of jarosite-type particle with trigonal antiprismatic morphology strongly depends on pH of the system. Trace of Fe2+ ions enter jarosite-type crystal and play a role in the development of the trigonal antiprismatic morphology. Based on the characterization data and experimental observation, the possible formation mechanism was clarified. Fe3+ ions firstly transformed to schwertmannite in the presence of SO42− ions. When Na+ (K+ or NH4+) ions coexist in the system, schwertmannite is preferable to transforming jarosite-type compounds instead of other iron oxides.