Zhaoyong Bian

Electrocatalytic degradation of 2,4-dichlorophenol using a Pd/graphene gas-diffusion electrode

Palladium-modified graphene gas-diffusion cathodes were prepared using Pd/graphene catalysts and characterized using cyclic voltammetry, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectrometry. The Pd particles were amorphous and had an average size of 5.4 nm, and were highly dispersed in the graphene. A diaphragm electrolysis system sequentially fed with H2 and air over the gas-diffusion cathodes was constructed, and applied to the degradation of 2,4-dichlorophenol (2,4-DCP). When the Pd/graphene gas-diffusion cathode was fed with hydrogen, reductive dechlorination of 2,4-DCP took place, whereas acceleration of two-electron reduction of O2 to H2O2 proceeded in air. Dechlorination of 2,4-DCP reached approximately 96.4% after 60 min, while its removal efficiency and its removal in terms of total organic carbon (TOC) reached approximately 100% and 90.5%, respectively, after 120 min. By analysis of the electrolysis products by HPLC and IC, a reaction pathway has been proposed for the degradation of 2,4-DCP.

Catalysis performance comparison for electrochemical reduction of CO2 on Pd–Cu/graphene catalyst

A Pd–Cu/graphene catalyst for the electrochemical reduction of CO2 was prepared by means of sodium borohydride reduction in a graphite oxide suspension with metal precursor salts, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), and current–time (I–t) scans technologies. The formation of Pd–Cu catalysts was investigated by changing the precursors and the Pd–Cu ratio. The results indicated that graphene with a d-spacing of 3.82 A was fabricated and Pd–Cu metal nanoparticles whose size ranges from 8 to 10 nm were highly dispersed on the graphene sheets with amorphous structure. Additionally, sharp increase of the reduction current under CO2 compared to that under N2 could be observed which contributed to the catalytic reaction of CO2 reduction on the Pd–Cu/graphene electrode. The best catalytic performance of the metal/graphene catalysts was achieved on 1 wt% Pd–2 wt% Cu/graphene, which had a relative positive peak potential and reduction current were −1.3 V (vs. Ag/AgCl) and −2.8 mA, respectively. The Pd–Cu/graphene electrode effectively suppressed the reaction process of hydrogen and showed stable CO2 reduction activity. Finally, the reaction pathway for the CO2 reduction on the Pd–Cu/graphene electrode was proposed.

Simultaneous removal of Cr(VI) and phenol contaminants using Z-scheme bismuth oxyiodide/reduced graphene oxide/bismuth sulfide system under visible-light irradiation

An all-solid-state Z-scheme system containing Bi-based semiconductors bismuth oxyiodide (BiOI) and bismuth sulfide (Bi2S3) was constructed on reduced graphene oxide (rGO) sheets through an electrostatic self-assembly method to simultaneously remove aqueous Cr(VI) and phenol. In this Z-scheme that mimicked natural photosynthesis, photoinduced electrons in the conduction band (CB) of BiOI were transferred through rGO and reacted with photoinduced holes in the valence band (VB) of Bi2S3, which significantly increased its photocatalytic activity. The reduction and oxidation reactions were performed on Bi2S3 and BiOI photocatalysts, respectively. Furthermore, complex contaminants of coexisting heavy metal Cr(VI) and organic phenol were treated using the system under visible-light irradiation. Results showed that Cr(VI) reduction and phenol oxidation were achieved efficiently with optimum reductive and oxidative efficiencies up to 73% and 95% under visible-light irradiation, respectively. This work provided a promising method of simultaneously removing heavy metals and organic pollutants by using a Z-scheme system with enhanced photocatalytic activity.

Morphological effect of BiVO4 catalysts on degradation of aqueous paracetamol under visible light irradiation

Morphological effect of bismuth vanadate (BiVO4) on visible light-driven catalytic degradation of aqueous paracetamol was carefully investigated using four monoclinic BiVO4 catalysts. The catalysts with different morphologies were controllably prepared by a hydrothermal method without any additions. The prepared catalysts were fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy (DRS). Under the visible light irradiation, these catalysts with different morphology were investigated to degrade aqueous paracetamol contaminant. The degradation effects were evaluated based on the catalyst morphology, solution pH, initial paracetamol concentration, and catalyst dosage. Cube-like BiVO4 powders exhibited excellent photocatalytic performance. The optimal photocatalytic performance of the cube-like BiVO4 in degrading paracetamol was achieved.

Comparative study on electrochemical 4-chlorophenol degradation in different diaphragm systems with combined reduction and oxidation properties

Two diaphragm electrolysis systems, two-electrode (anode-cathode) and three-electrode (cathode-anode-cathode), were compared for the electrochemical degradation of 4-chlorophenol. The performance of these systems was improved by feeding with hydrogen gas and then with air, in aid of the combined processes of reduction and oxidation. The 4-chlorophenol degradation, dechlorination, and total organic carbon removal were monitored to characterize the difference between the two systems. The results indicated that the three-electrode system exhibited higher degradation percentages for 4-chlorophenol compared with that of the two-electrode system. The dechlorination property of the three-electrode system was stronger than that of the two-electrode system. In addition, the total organic carbon removal percentage of the anodic compartment in the three-electrode system was higher than that of the two-electrode system. The three-electrode system showed excellent treatment properties for 4-chlorophenol.

Electrocatalytic degradation kinetic of 4-chlorophenol by the Pd/C gas-diffusion electrode system

A Pd/C gas-diffusion cathode which generated H2O2 through a two-electron reduction process of fed oxygen molecule was used to degrade 4-chlorophenol in an undivided electrolysis device. The kinetics of 4-chlorophenol degradation has been investigated by the electrochemical oxidation processes. By inspecting the relationship between the rate constants (k) and influencing factors, using first-order kinetics to describe the electrochemical oxidation process of 4-chlorophenol, a kinetic model of 4-chlorophenol degradation process was proposed to calculate the 4-chlorophenol effluent concentration: C = C0 exp( -3:76 × 10(-6) C(-0.5)0 J(2) M(-0.7) Q(0.17) Dt). It was found that the electrocatalytic degradation rate of 4-chlorophenol was affected by current density, electrode distance, air-feeding rate, electrolyte concentration and initial 4-chlorophenol concentration. The kinetics obtained from the experiments under corresponding electrochemical conditions could provide an accurate estimation of 4-chlorophenol effluent concentration and lead to better design of the electrochemical reactor.

Treatment of methyl orange dye wastewater by cooperative electrochemical oxidation in anodic–cathodic compartment

Electrochemical oxidation of methyl orange wastewater was studied using Ti/IrO(2)/RuO(2) anode and a self-made Pd/C O(2)-fed cathode in the divided cell with a terylene diaphragm. The result indicated that the appropriate rate of feeding air improved the methyl orange removal efficiency. The discoloration efficiency of methyl orange in the divided cell increased with increasing current density. The initial pH value had some effect on the discoloration of methyl orange, which became not obvious when the pH ranged from 2 to 10. However, the average removal efficiency of methyl orange wastewater in terms of total organic carbon (TOC) can reach 89.3%. The methyl orange structure had changed in the electrolytic process, and the characteristic absorption peak of methyl orange was about 470 nm. With the extension of electrolysis time, the concentration of methyl orange gradually reduced; wastewater discoloration rate increased gradually. The degradation of methyl orange was assumed to be cooperative oxidation by direct or indirect electrochemical oxidation at the anode and H(2)O(2), ·OH, O(2)(-)· produced by oxygen reduction at the cathode in the divided cell. Therefore, the cooperative electrochemical oxidation of methyl orange wastewater in the anodic-cathodic compartment had better degradation effects.

Degradation of 4-chlorophenol by the anodic–cathodic cooperative effect with a Pd/MWNT gas-diffusion electrode

Pd/multi-walled carbon nanotubes (MWNTs) catalyst used for the gas-diffusion electrode was prepared by ethylene glycol (EG) reduction and characterized by the X-ray diffraction (XRD) and scanning electron microscope (SEM). The results indicated that Pd particles with an average size of 8.0 nm were highly dispersed in the MWNTs with amorphous structure. In a diaphragm electrolysis system with a Ti/RuO(2)/IrO(2) anode and the Pd/MWNT gas diffusion cathode, the degradation of 4-chlorophenol was performed by a combination of electrochemical reduction and oxidation. The combined process was in favor of improving 4-chlorophenol degradation efficiency. The optimum reaction conditions were as following: initial pH 7, aeration with hydrogen and air. Under the optimized electrolysis conditions the removal of 4-chlorophenol in the anodic and cathodic compartments were 98.5 and 90.5%, respectively. Additionally, based on the analysis of electrolysis intermediates using high performance liquid chromatography (HPLC) and ion chromatography (IC), the electrolysis degradation of 4-chlorophenol was proposed containing the intermediates, such as phenol, hydroquinone, benzoquinone, maleic acid, fumaric acid, succinic acid, malonic acid, oxalic acid, acetic acid and formic acid.

Cadmium ion adsorption by amine-modified activated carbon

Cadmium (Cd) is one of the most toxic metals found in water and sediments. In the effort to develop an effective adsorbent for aqueous Cd removal, activated carbon (AC) was modified with an amino-terminated organosilicon (3-aminopropyltrimethoxysilane, APS). Response surface methodology was used to optimize selected operational parameters of adsorption of aqueous Cd by considering a central composite design with three input variables, temperature of the mixture solution, the contact time and feed ratio (APS/AC), on the surface modification. Results demonstrated that the strong Cd-binding amine ligands were effectively introduced onto the AC surfaces through the silanol reaction between carbon surface functional groups (-COOH, -COH) and APS molecules. The optimized preparation condition is 77 °C, 4 h and 2.1 ratio. The adsorbent presented a favorable adsorption of the aqueous Cd(II).