Jianhui Sun

Recent developments in heterogeneous photocatalytic water treatment using visible light-responsive photocatalysts: a review

Visible light-responsive photocatalytic technology holds great potential in water treatment to enhance purification efficiency, as well as to augment water supply through the safe usage of unconventional water sources. This review summarizes the recent progress in the design and fabrication of visible light-responsive photocatalysts via various synthetic strategies, including the modification of traditional photocatalysts by doping, dye sensitization, or by forming a heterostructure, coupled with π-conjugated architecture, as well as the great efforts made within the exploration of novel visible light-responsive photocatalysts. Background information on the fundamentals of heterogeneous photocatalysis, the pathways of visible light-responsive photocatalysis, and the unique features of visible light-responsive photocatalysts are presented. The photocatalytic properties of the resulting visible light-responsive photocatalysts are also covered in relation to the water treatment, i.e., regarding the photocatalytic degradation of organic compounds and inorganic pollutants, as well as photocatalytic disinfection. Finally, this review concludes with a summary and perspectives on the current challenges faced and new directions in this emerging area of research.

Photocatalytic degradation of Orange G on nitrogen-doped TiO2 catalysts under visible light and sunlight irradiation

In this paper, the degradation of an azo dye Orange G (OG) on nitrogen-doped TiO2 photocatalysts has been investigated under visible light and sunlight irradiation. Under visible light irradiation, the doped TiO2 nanocatalysts demonstrated higher activity than the commercial Dugussa P25 TiO2, allowing more efficient utilization of solar light, while under sunlight, P25 showed higher photocatalytic activity. According to the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis spectra analyses, it was found that both the nanosized anatase structure and the appearance of new absorption band in the visible region caused by nitrogen doping were responsible for the significant enhancement of OG degradation under visible light. In addition, the photosensitized oxidation mechanism originated from OG itself was also considered contributing to the higher visible-light-induced degradation efficiency. The effect of the initial pH of the solution and the dosage of hydrogen peroxide under different light sources was also investigated. Under visible light and sunlight, the optimal solution pH was both 2.0, while the optimal dosage of H2O2 was 5.0 and 15.0 mmol/l, respectively.

Decolorization of an azo dye Orange G in aqueous solution by Fenton oxidation process: Effect of system parameters and kinetic study

To establish cost-efficient operating conditions for potential application of Fenton oxidation process to treat wastewater containing an azo dye Orange G (OG), some important operating parameters such as pH value of solutions, dosages of H(2)O(2) and Fe(2+), temperature, presence/absence of chloride ion and concentration of the dye, which effect on the decolorization of OG in aqueous solution by Fenton oxidation have been investigated systematically. In addition, the decolorization kinetics of OG was also elucidated based on the experimental data. The results showed that a suitable decolorization condition was selected as initial pH 4.0, H(2)O(2) dosage 1.0 x 10(-2)M and molar ratio of [H(2)O(2)]/[Fe(2+)] 286:1. The decolorization of OG enhanced with the increasing of reaction temperature but decreased as a presence of chloride ion. On the given conditions, for 2.21 x 10(-5) to 1.11 x 10(-4)M of OG, the decolorization efficiencies within 60 min were more than 94.6%. The decolorization kinetics of OG by Fenton oxidation process followed the second-order reaction kinetics, and the apparent activation energy E, was detected to be 34.84 kJ mol(-1). The results can provide fundamental knowledge for the treatment of wastewater containing OG and/or other azo dyes by Fenton oxidation process.

Microwave-assisted preparation, characterization and photocatalytic properties of a dumbbell-shaped ZnO photocatalyst.

A novel dumbbell-shaped ZnO photocatalyst was successfully synthesized by microwave heating in the present study. The prepared ZnO photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis absorption spectrum (UV-Vis). The results indicated that the prepared ZnO photocatalyst shows a united dumbbell shape with 2 microm diameter and 5 microm length. The photocatalytic activity of the prepared dumbbell-shaped ZnO photocatalyst was evaluated by the degradation of Methylene Blue (MB) in aqueous solution. The effects of pH, catalyst dosage ([ZnO]) and initial concentration of MB ([MB]) on the photocatalytic degradation efficiency of MB were investigated. An optimum condition was determined as pH 7-8, [ZnO]=1.0 g-ZnO L(-1) and [MB]=15 mg-MB L(-1). Under the optimum condition, the decolorization and TOC removal efficiencies of MB at 75 min reaction time were achieved 99.6% and 74.3%, respectively, which were higher than that by the commercial ZnO powder. In addition, the photocatalytic degradation kinetics of MB was also investigated. The results showed that the photocatalytic degradation kinetics of MB fitted the pseudo-first-order kinetics and the Langmuir-Hinshelwood model.

Preparation and photocatalytic property of a novel dumbbell-shaped ZnO microcrystal photocatalyst

A novel dumbbell-shaped ZnO microcrystal photocatalyst was successfully synthesized by hydrothermal method in the present study. The prepared ZnO photocatalyst was systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG-DTA), photoluminescence spectrum (PL) and UV-vis absorption spectrum (UV-vis). The characterizations of dumbbell-shaped ZnO were also compared with the commercial ZnO. The results show that the prepared ZnO photocatalyst has a unique dumbbell shape and it belongs to the hexagonal wurtzite family. In addition, the photocatalytic activity of the prepared dumbbell-shaped ZnO microcrystal photocatalyst was evaluated by the degradation of three different kinds of dyes wastewater (Crystal Violet, Methyl Violet and Methylene Blue). After 75 min reaction, the decolourization efficiencies of the three kinds of dyes wastewater achieved 68.0%, 99.0% and 98.5%, the TOC removal efficiencies achieved 43.2%, 59.4% and 70.6%, respectively. Compared to commercial ZnO, 16-22% higher TOC removal efficiency was obtained by the dumbbell-shaped ZnO. The results indicated that the prepared dumbbell-shaped ZnO microcrystal photocatalyst showed good photocatalytic activity and it could be considered as a promising photocatalyst for dyes wastewater treatment.

Distribution of Polycyclic aromatic hydrocarbons (PAHs) in Henan Reach of the Yellow River, Middle China

The distribution and source of 16 polycyclic aromatic hydrocarbons (PAHs) in Henan Reach of the Yellow River, Middle China, has been investigated. summation sigmaPAHs levels ranged from 144.3 to 2361 ng L(-1) in water, from 506.6 to 10,510 ng g(-1) in suspended particulate matters (SPMs) and from 16.4 to 1358 ng g(-1) in sediment, respectively. The compositional profile of PAHs revealed that 2-3-ring PAHs were predominated in water and 2-4-ring PAHs were abundant in SPMs. Whereas the PAHs in sediment were composed mainly of 3-5-ring PAHs. The spatial distribution of PAHs indicated that concentrations of PAHs in water and SPMs in dry season were much higher than those in flooding season. It may be attributed to a high flow rate in flooding season. The ratios of phenanthrene/anthracene (Phe/Ant) and fluoranthene/pyrene (Flua/Pyr) reflected a pattern of pyrogenic input. The potential ecosystem risk assessment indicated that the ecosystem risk of PAHs was relatively low in Henan Reach of the Yellow River.

Distribution and sources of organochlorine pesticides (OCPs) in sediments from upper reach of Huaihe River, East China

Residues of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) and their environmental risks in surface sediments collected from upper reach of Huaihe River, East China, are investigated in this paper. Based on dry weight (dw), the concentrations of ΣHCH (α-, β-, γ- and δ-HCH) and ΣDDT (p,p-DDT, o,p-DDT, p,p-DDE, p,p-DDD) in sediments ranged from 1.95 to 11.05 ng g(-1) dw (mean 4.53 ng g(-1)dw) and 4.07 to 23.89 ng g(-1)dw (average 11.07 ng g(-1)dw), respectively. Compared with some published guideline values of organochlorine pesticides (OCPs) in sediments, the concentrations of HCHs were at safe levels while the residues of DDTs would pose adverse biological effects in this studied area. The distribution of OCPs in sediments indicated that the input of tributaries was important factor for Huaihe River. Levels of DDTs in the sediments were influenced by total organic carbon contents of sediments. The present study suggested that historical usage of lindane and technical DDT was the main reason for OCP residues in the sediments from both rivers and lakes. Furthermore, the composition of DDTs reflected fresh inputs of dicofol mixture in this region.

Residues of organochlorine pesticides (OCPs) in upper reach of the Huaihe River, East China.

Residues of HCHs and DDTs in surface water and suspended particulate matter (SPM) from upper reach of the Huaihe River, East China, were investigated. Levels of total HCHs (∑HCH) and total DDTs (∑DDT) in water detected by GC-ECD ranged from 0.85 to 12.77 ng L⁻¹ and from 3.54 to 33.59 ng L⁻¹, respectively. According to European and America water quality guidelines, HCHs were within safe levels while DDT would pose adverse biological effects. Distribution of OCPs in water indicated that input of tributaries was important factor for the Huaihe River. For OCPs in SPM, concentrations varied from 1.01 to 25.22 ng g⁻¹ for ∑HCH and not detected to 4.74 ng g⁻¹ for ∑DDT. Compared with sediment quality guidelines, HCHs and DDTs might have an ecological risk. The main reason for OCPs residues in the Huaihe River was usage of lindane and technical DDT. Furthermore, composition of DDTs reflected fresh inputs of dicofol mixture in some sites.

Effective removal of heavy metals from industrial sludge with the aid of a biodegradable chelating ligand GLDA.

Tetrasodium of N,N-bis(carboxymethyl) glutamic acid (GLDA), a novel readily biodegradable chelating ligand, was employed for the first time to remove heavy metals from industrial sludge generated from a local battery company. The extraction of cadmium, nickel, copper, and zinc from battery sludge with the presence of GLDA was studied under different experimental conditions such as contact times, pH values, as well as GLDA concentrations. Species distribution of metals in the sludge sample before and after extraction with GLDA was also analyzed. Current investigation showed that (i) GLDA was effective for Cd extraction from sludge samples under various conditions. (ii) About 89% cadmium, 82% nickel and 84% copper content could be effectively extracted at the molar ratio of GLDA:M(II)=3:1 and at pH=4, whereas the removal efficiency of zinc was quite low throughout the experiment. (iii) A variety of parameters, such as contact time, pH values, the concentration of chelating agent, stability constant, as well as species distribution of metals could affect the chelating properties of GLDA.

Layer-by-layer construction of graphene-based microbial fuel cell for improved power generation and methyl orange removal

Development of highly efficient anode is critical for enhancing the power output of microbial fuel cells (MFCs). The aim of this work is to investigate whether modification of carbon paper (CP) anode with graphene (GR) via layer-by-layer assembly technique is an effective approach to promote the electricity generation and methyl orange removal in MFCs. Using cyclic voltammetry and electrochemical impedance spectroscopy, the GR/CP electrode exhibited better electrochemical behavior. Scanning electron microscopy results revealed that the surface roughness of GR/CP increased, which was favorable for more bacteria to attach to the anode surface. The MFCs equipped with GR/CP anode achieved a stable maximum power density of 368xa0mWxa0m−2 under 1,000 Ω external resistance and a start time for the initial maximum voltage of 180xa0h, which were, respectively, 51xa0% higher and 31xa0% shorter than the corresponding values of the MFCs with blank anode. The anode and cathode polarization curves revealed negligible difference in cathode potentials but obviously difference in anode potentials, indicating that the GR-modified anode other than the cathode was responsible for the performance improvement of MFC. Meanwhile, compared with MFCs with blank anode, 11xa0% higher decolorization efficiency and 16xa0% higher the chemical oxygen demand removal rate were achieved in MFC with GR-modified anode during electricity generation. This study might provide an effective way to modify the anode for enhanced electricity generation and efficient removal of azo dye in MFCs.