Synthesis of CuO–GO/TiO2 visible light photocatalyst for 2-chlorophenol degradation, pretreatment of dairy wastewater and aerobic digestion

Graphene-based photocatalysts for degradation of organic pollution

Compared with the traditional wastewater treatment technology, semiconductor photocatalysis is a rapidly emerging environment-friendly and efficient Advanced Oxidation Process for degradation of refractory organic contaminants. Single-component semiconductor photocatalysts exhibit poor photocatalytic performance and cannot meet the requirements of wastewater treatment. The combination of semiconductor photocatalysts and Graphene can effectively improve the photocatalytic activity and stability of semiconductor photocatalysts. This review focuses on the synergistic effect of several types of semiconductors with Graphene for photocatalytic degradation of organic pollutants. After a brief introduction of the photodegradation mechanism of semiconductor materials and the basic description of Graphene, the synthesis, characterization and degradation performance of various Graphene-based semiconductor photocatalysts are emphatically introduced.

From waste to waste: iron blast furnace slag for heavy metal ions removal from aqueous system

Inordinate levels of heavy metals in water sources have long been a matter of concern, posing serious environmental and public health risks. Adsorption, on the other hand, is a viable technique for removing heavy metals from water due to its high efficiency, low cost, and ease of operation. Blast furnace slag (BFS) is considered a cheap sorbent for the get rid of Co²⁺ and Pb²⁺ ions from aqueous media. The nonmodified slag is characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), N₂ adsorption-desorption isotherms, energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and zeta potential. The removal of Co²⁺ and Pb²⁺ ions was carried out using batch adsorption experiments from an aqueous medium. The influence of several variables as pH, contact time, adsorbent dose, temperature, and initial ions concentration was considered. The isotherm, kinetic, thermodynamic, and recyclability were also conducted. The maximum uptake capacity for Co²⁺ and Pb²⁺ was 43.8 and 30.2 mg g^-1 achieved at pH 6 after 60 min contact time. The adsorption kinetics and isotherms of BFS for Co²⁺ and Pb²⁺ fitted well to Avrami and Freundlich models, respectively. The main adsorption mechanism between BFS and the metal ions was ion exchange. The regeneration of the used slag was studied for reuse many cycles. In terms of economics and scalability, nonmodified BFS treatment has great potential as a cost-effective adsorbent that could be used in water pollution treatment.

Zinc ferrite nanoparticles from industrial waste for Se (IV) elimination from wastewater

The presence of high concentrations of selenium ions in wastewater is considered an environmental problem. However, the mechanism of selenium ions (Se (IV)) removal by the adsorption process has not been investigated in-depth so far. Also, the recovery and conversion of the industrial waste materials into valuable materials is a vital issue. Therefore, in this study, zinc ferrite nanopowders are economically synthesized from steel-making wastes by co-precipitation method for investigating as adsorbents of selenium species. The produced nanopowders were annealed at 150, 300, 500, and 850 °C for 5 h to scrutinize the impact of annealing temperature on their crystallite size. The compositional, optical, and magnetic features of the nanopowders were defined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), UV-Vis. spectrophotometer along with vibrating sample magnetometer (VSM). Optical absorbance spectra were found characteristic due to the electronic structure of Fe³⁺ (3d⁵) considering the C_3v local symmetry of Fe³⁺ ions. The prepared nanopowders demonstrated good adsorption capacity toward selenium ions (43.67 mg/g at pH 2.5) from an aqueous medium. Adsorption data were found fitting to Freundlich isotherm model. Thus, ZnFe₂O₄ can be recommended to effectively eliminate selenium ions from aqueous solutions.

Development of a semiconductor tree branch-like photoreactor for textile industry effluent treatment

This paper aimed to develop a new photocatalytic reactor design with a rotary tree branch structure for wastewater treatment in the textile industry. The brass sheet calcined at 500 °C (B500) was used as the photocatalyst and as a substrate for ZnO nanoparticle immobilization (B500ZnO). The photoreactor performance was evaluated toward the photodegradation of an aqueous solution of Reactive Black 5 dye (AS-RB5), raw wastewater (RW), and treated wastewater (TW). X-ray diffraction (XRD) and scanning electron microscopy (SEM) results illustrated ZnO nanowire formation over B500 and B500ZnO substrates. The bandgap values of these samples were estimated by diffuse reflectance measurements. The effects of dye concentration, the type of radiation, and ZnO NP deposition on the degradation of AS-RB were evaluated. Decreases in chemical oxygen demand (COD) greater than 82% were obtained using solar irradiation and artificial light as the energy source. Regarding calcined brass sheet reutilization, a decrease of 45% in the photocatalytic activity efficiency after 5 cycles was noted due to the effect of photocorrosion of the ZnO nanowires. The photoreaction of the RW and TW effluents showed COD values of 21 and 35%, respectively, which are below the limits established by state environmental control. With respect to RB5 addition to the TW effluent (TW-RB5), a discoloration of 62% was noticed after 3 h of photodegradation. Furthermore, the toxicity tests of the AS-RB5 and TW-RB5 samples did not display toxic intermediates after the photoreaction since 80% of the seeds germinated. Finally, the photoreactor exhibited good performance regarding the decrease in effluent pollutant charge, in addition to the efficient discoloration of RB5 dye.

Photoelectrochemical Water-Splitting Using CuO-Based Electrodes for Hydrogen Production: A Review

The cost-effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water-splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO-based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water-splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO-based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent-generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.

A novel tubular up-flow magnetic film photocatalytic system optimized by main factors control for efficient removal of chlorophenols wastewater

Chlorophenols (CPs) are still used as raw material or intermediate in some industries. Photocatalytic oxidation is free from secondary pollution, but the efficiency is restricted by some main factors. In this study, a novel high efficiency tubular up-flow magnetic film (TUMF) photocatalytic system was investigated based on the magnetic lanthanum doping core-shell Fe₃O₄@SiO₂@TiO₂ (La-FST) nanoparticles. When the dosage of La-FST was 0.4 g/L, the flow velocity was 94.2 mL/min, and the circulated irradiation of 15 W maintained 40 min, the average removal rate of 2,4-dichlorophenol (2,4-DCP) was reduced significantly from 10 mg/L to 0.0803 mg/L by TUMF system, meeting the limits of the particular items (0.093 mg/L) from national environmental quality standards for surface water, avoiding the problem of photocatalyst separation and loss. The photoinduced holes (h⁺) was the key active radical to oxidize 2,4-DCP, and the main factors of TUMF system could be well controlled to achieve satisfactory effluent quality. A prediction method of photocatalytic reaction time in a multistage series TUMF system was established to remove 2,4-DCP from 100 mg/L to 0.5 mg/L, saving 86 min. The novel high-efficiency TUMF system provides a technical selection for the photocatalytic degradation of CPs and other refractory organics.

Bio-photoelectrochemcial system constructed with BiVO4/RGO photocathode for 2,4-dichlorophenol degradation: BiVO4/RGO optimization, degradation performance and mechanism

A single-chamber bio-photoelectrochemical system (BPES) constructed with BiVO₄/reduced graphene oxide (RGO) photocathode was proposed for 2,4-dichlorophenol (2,4-DCP) degradation under simulated solar irradiation. The BiVO₄/RGO (B/G) composites were synthesized, optimized and characterized by various techniques to analyze their physico-chemical and photocatalytic properties. Results showed that B/G (5 wt% - 9 h - 150 °C) exhibited the best photocatalytic activity for 2,4-DCP degradation, which was 1.5 times of that of BiVO₄, due to its better light absorption, faster electrons transfer, and more efficient photo-generated e^- - h⁺ separation. Reactive species trapping experiments revealed that ·OH was the main radical leading to 2,4-DCP degradation, and h⁺ also influenced 2,4-DCP removal. The 2,4-DCP (20 mg/L) removal rate and current output from the illuminated BPES were much higher than those of the unilluminated reactor (68.5 % vs. 41.8 %, 60.31 A/m³ vs. 40.07 A/m³) in 24 h, and the cathode potential was more negative, indicating that photocathode catalytic process was favorable to pollutants degradation and energy generation. Intermediates of 2,4-DCP degradation in the BPES were identified, and accordingly, possible degradation pathway and mechanism were proposed. This research advanced the development of efficient photocathode and mechanism of recalcitrant wastewater treatment in the BPES.