Dual-function hydrogel composite for post-electroplating cationic and anionic metal removal: A practicality study.

Metals produced as by-products of the electroplating process pose threats to both human and environmental health, so it is important that they are removed from electroplating effluents. In this study, a dual-function hydrogel composite, prepared from a pair of cationic and anionic hydrogel composites via a facile method, was tested in batch and in a fluidized-bed column to treat a simulated electroplating effluent. For the batch treatment, both adsorption and desorption reached equilibrium within 30 min, showing the dual-function composite's fast adsorption capacity. Additionally, the removal efficiency was found to be pH-independent, and insignificant effect was found in the co-presence of monovalent ions (up to 10 meq L-1). Reusability of the dual-function composite was tested for six cycles, where the treated effluent consistently met discharge standards, and the reused adsorbent was confirmed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy to be highly stable. The fast settling by gravity of the dual-function composite in batch motivated further studies of the material in a fluidized-bed column. Process variables such as feed flow, airflow, and adsorbent's bed depth were optimized using response surface methodology (RSM). Using an optimal solution, the model predicted a treatable cationic volume of 1045 mL and an anionic volume of 1695 mL; their corresponding experimental values were 1028 and 1680 mL. Therefore, in terms of practicality (fast removal, pH-independence, high stability, and gravity-driven settling), the application of the dual-function composite in a fluidized-bed reactor has shown much promise for the simultaneous removal of post-electroplating cationic and anionic metals.

Visible-light-driven peroxymonosulfate activation in photo-electrocatalytic system using hollow-structured Pt@CeO2@MoS2 photoanode for the degradation of pharmaceuticals and personal care products.

In this study, we constructed an innovative photo-electrocatalysis-assisted peroxymonosulfate (PEC/PMS) system to degrade pharmaceuticals and personal care products (PPCPs). A hollow-structured photoanode (i.e., Pt@CeO2@MoS2) was specifically synthesized as a photoanode to activate PMS in the PEC system. As proof of concept, the Pt@CeO2@MoS2 photoanode exhibited superior degradation performance toward carbamazepine (CBZ) with PMS assistance. Specifically, the kinetic constant of PEC/PMS (k = 0.13202 min-1) could be enhanced about 87.4 times compared to that of the PEC system (0.00151 min-1) alone. The PMS activation mechanism revealed that the synergistic effect between the hollow material and the change of surface valence states (Ce3+ to Ce4+) and (Mo4+ to Mo6+) contribute to enhancing the degradation efficiency of the visible-light-driven PEC/PMS process. The scavenger testing and EPR showed that 1O2, O2•-, SO4•- and •OH play dominant roles in the SR-AOPs. Furthermore, the applicability of Pt@CeO2@MoS2 used in SR-AOPs was systematically investigated regarding of the reaction parameters and identification of intermediates and dominant radicals as well as the mineralization rate and stability. The outcomes of this study can provide a new platform for environmental remediation.

Role of surface functional groups of hydrogels in metal adsorption: From performance to mechanism.

Hydrogels have been studied quite intensively in recent decades regarding whether their metal adsorption abilities may be modified or even enhanced via functionalization (i.e., functionalizing the surfaces of hydrogels with specific functional groups). Studies have found that functionalizing hydrogels can in fact give them higher adsorptive power. This enhanced adsorptive performance is articulated in this paper through critically reviewing more than 120 research articles in such terms as the various techniques of synthesizing functionalized hydrogels, the roles that specific functional groups play on adsorption performance, selectivity, reusability, as well as on adsorption mechanism. Moreover, this critical review offers insight into future designs of functionalized hydrogels with specific metal adsorption capabilities.

An innovative pH-independent magnetically separable hydrogel for the removal of Cu(II) and Ni(II) ions from electroplating wastewater.

A novel magnetic anionic hydrogel (nFeMAH), synthesized via a facile method, was characterized by XRD, VSM, SEM, TEM, FTIR, XPS, and ζ-potential measurement. Over the tested range of pH 2 to 12, the surface of the nFeMAH was permanently negative with a ζ-potential of -35 to -45 mV. The adsorption kinetics and capacity of nFeMAH were studied. Within 60 min, equilibrium was achieved with maximum adsorption capacities of 102 mg Cu(II)/g and 93 mg Ni(II)/g. The pseudo-second-order kinetics model was well-matched with the experimental data, whereas the Langmuir isotherm model agreed well with the isotherm data. The magnetic separation efficiency of nFeMAH remained above 90% after 20 cycles of adsorption-desorption, whereas the Ni(II) removal efficiency dropped from 92 to about 75% after the first cycle. The magnetic separation efficiency of nFeMAH was consistently high (99%). The major mechanism of metal removal by nFeMAH was ion exchange but there also was evidence for formation of metal oxides. Therefore, the application of nFeMAH for treating electroplating wastewater can be a desirable option when considering its superior performance in the adsorptive treatment, i.e., pH insensitivity, fast adsorption kinetics, high reusability, and consistency in magnetic separation.