In the present study, a new type of montmorillonite/carbon (MMT/C) adsorbent has been prepared by a one-pot hydrothermal carbonization process. The MMT/C composite was further modified to obtain functionalized MMT/C, i.e., hydroxylated MMT/C, carboxylated MMT/C, and aminated MMT/C. The prepared MMT/C-based sorbents were systematically characterized by X-ray diffraction (XRD), specific surface area, zeta potential, and scanning electron microscopy (SEM). Their adsorption capacity was evaluated by the removal of aqueous Pb(II) ions, following the order carboxylated MMT/C > hydroxylated MMT/C > aminated MMT/C > MMT/C. Moreover, the influential factors for Pb(II) removal by carboxylated MMT/C composites, such as pH, temperature, and initial concentration, were thoroughly explored. The adsorption capacity increases significantly when the pH increases from 2.0 to 5.0 but with minor change beyond. The maximum adsorption capacities of MMT/C–COOH toward Pb(II) are 247.85 mg g–1. The complexation of surface groups such as −COOH on MMT/C–COOH might be responsible for Pb(II) sorption. The adsorption kinetic follows a pseudo-second-order model, and thermodynamic analysis implies an endothermic and spontaneous chemisorption process. The overall results suggest that the obtained composites are promising as an adsorbent for effective removal of Pb(II) from water.

The soluble redox mediator had been employed for catalyzing anaerobic bio-reduction of recalcitrant contaminants such as azo compounds (mainly azo dyes), nitroaromatics, halogenated pollutants and high valence heavy metal, etc. However, the continuous dosing of soluble redox mediators would not only be economically unreasonable, but also have a risk of causing secondary pollution. Therefore the insoluble/immobilized redox mediators were widely studied in last decades trying to overcome above drawbacks. This paper reviewed insoluble redox mediators including carbonaceous (activated carbon, emerging activated carbon fiber, carbon nanotubes, graphene oxide and biochar) and natural materials (humin and henna plant), as well as immobilized redox mediators such as immobilizing model quinones or humic acid on calcium alginate, polyurethane foam, Poly(ethylene terephthalate) fiber, anion exchange resin, etc. The catalyzing performance, characteristics, disadvantages (if any) and lab-scale applications of those insoluble/immobilized RMs were critically discussed, in order to provide reference for the evolvement and promoting further utilizations of novel insoluble/immobilized redox mediators. In addition, future research needed was suggested towards the engineering application of insoluble/immobilized redox mediators.

Novel hierarchical copper oxide (CuXO) nanosphere particles are synthesized, and then coated onto gas diffusion layer (carbon) to form a working electrode for catalyzing CO2 electroreduction. When applying a negative voltage to the working electrode, the metal Cu nanoparticles which are induced by the CuXO nanospheres appear. CuXO and metal Cu together form the CuXO/Cu nanocatalysts which show high catalytic activity for CO2 electroreduction. The morphology, composition, crystal structure and surface area of the CuXO/Cu electrocatalysts are characterized using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CuXO/Cu nanoparticles are tested as the catalysts for CO2 electroreduction using cyclic voltammetry and linear sweep voltammetry in CO2-saturated 0.5 M KHCO3 aqueous electrolyte. It is found that the CO2 electroreduction activity is highly improved using this CuXO/Cu nanocatalyst, which remains stable during 20 h of electrolysis, along with the high selectivity with a ∼62% of Faradaic efficiency for formate production. Detailed kinetic information relevant to the catalysis is also discussed.

Various CuxO catalysts with different special microstructures were synthesized using a simple one-step hydrothermal method by controlling the reaction time and temperature conditions. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) were used to observe the morphologies of the received catalysts. The 3-dimensional (3D) hierarchical nanospheres (500 nm) comprised of secondary structured nanorods (50 nm) are formed at 180 °C for 2 hours. However, when increasing the hydrothermal reaction temperature to 220 °C, solid microspheres with a large size of 2.5 μm begin to appear instead of flabby hierarchical nanospheres. To further investigate the effect of morphologies on the activity and production selectivity of CuxO catalysts, cyclic voltammetry (CV) was used to evaluate the onset potential and current density of catalyzed CO2 reduction combining linear sweep voltammetry (LSV) in 0.5 M KHCO3 solution. The effect of catalyst loading was also tested by applying the gas diffusion layer (GDL) to make up a working electrode for CO2 electroreduction. The results indicate that the synthesized temperature of 180 °C for 2 h is the optimal condition for CuxO nanospheres and the optimal loading is about 3 mg cm−2, under which the onset potential for CO2 electroreduction reaches −0.55 V vs. SHE. By ion chromatography measurement, the faradaic efficiency and production rate of produced formate was found to be 59%, which is much higher than most reported Cu-based catalysts at the same electrolysis conditions, indicating the high selectivity of the CuxO nanospheres due to their controlled special surface morphology.