Highly efficient solar-light-driven photocatalytic degradation of pollutants in petroleum refinery wastewater on hierarchically-structured copper sulfide (CuS) hollow nanocatalysts

Advances on sonophotocatalysis as a water and wastewater treatment technique: efficiency, challenges and process optimisation

Due to water shortage and increased water pollution, various methods are being explored to improve water quality by treating contaminants. Sonophotocatalysis is a combination of two individual water treatment processes i.e., photocatalysis and sonocatalysis. With advantages including shorter reaction times and enhanced activity, this technique shows possible futuristic applications as an efficient water treatment technology. Herein, background insight on sonophotocalysis as a water and wastewater treatment technique as well as the general mechanism of activity is explained. The commonly used catalysts for sonophotocatalytic applications as well as their synthesis pathways are also briefly discussed. Additionally, the utilisation of sonophotocatalysis for the disinfection of various microbial species as well as treatment of wastewater pollutants including organic (dyes, pharmaceuticals and pesticides) and inorganic species (heavy metals) is deliberated. This review also gives a critical analysis of the efficiency, enhancement strategies as well as challenges and outlooks in this field. It is thus intended to give insight to researchers in the context of facilitating future developments in the field of water treatment, and advancing sonophotocatalysis towards large-scale implementation and commercialization.

Application of photocatalytic proxone process for petrochemical wastewater treatment

Industrial wastewaters are different from sanitary wastewaters, and treatment complications due to their unique characteristics, so biological processes are typically disrupted. High chemical oxygen demand, dye, heavy metals, toxic organic and non-biodegradable compounds present in petroleum industry wastewater. This study intends to optimize the photocatalytic proxone process, utilizing a synthesized ZnO-Fe3O4 nanocatalyst, for petroleum wastewater treatment. The synthesis of ZnO-Fe3O4 was done by air oxidation and layer-by-layer self-assembly method and XRD, SEM, EDAX, FT-IR, BET, DRS, and VSM techniques were used to characterize the catalyst. Central composite design (CCD) method applied to investigated the effect of pH (4-8), reaction time (30-60 min), ozone gas concentration (1-2 mg/L-min), hydrogen peroxide concentration (2-3 mL/L) and the amount of catalyst (1-0.5 g/L) on the process. In the optimal conditions, biological oxygen demand (BOD5) and total petroleum hydrocarbon (TPH) removal, reaction kinetic, and synergistic effect mechanisms on the process were studied. Based on the ANOVA, a quadratic model with R2 = 0.99, P-Value = 0.0001, and F-Value = 906.87 was proposed to model the process. Based on the model pH = 5.7, ozone concentration = 1.8 mg/L-min, hydrogen peroxide concentration = 2.5 mL/L, reaction time = 56 min, and the catalyst dose = 0.7 g/L were proposed as the optimum condition. According to the model prediction, an efficiency of 85.3% was predicted for the removal of COD. To evaluate the accuracy of the prediction, an experiment was carried out in optimal conditions, and experimentally, a 52% removal efficiency was obtained. Also, at the optimum condition, BOD5 and TPH removal were 91.1% and 89.7% respectively. The reaction kinetic follows the pseudo-first-order kinetic model (R2 = 0.98). Also, the results showed that there is a synergistic effect in this process. As an advanced hybrid oxidation process, the photocatalytic proxone process has the capacity to treat petroleum wastewater to an acceptable standard.

Synthesis of triethylenetetramine modified sodium alginate/CuS nanocrystal composite for enhanced Cr(VI) removal: Performance and mechanism

Photocatalysis has been widely used for the removal of hexavalent chromium from wastewater as an efficient and environmental friendly method. However, conventional photocatalysts generally exhibit poor adsorption properties toward Cr(VI), resulting in unsatisfactory performance in high concentrated wastewaters. In this study, we synthesized a novel composite material with high Cr(VI) adsorption ability by blending prepared CuS nanocrystals into triethylenetetramine modified sodium alginate for the enhanced photocatalytic removal of Cr(VI). Effect of CuS dosage, pH value, light source and intensity were discussed for the optimum Cr(VI) removal conditions. The synthesized composite has shown good adsorption performance toward Cr(VI) and the overall removal rate reached 98.99 % within 50 min under UV light irradiation with citric acid as hole scavenger. Adsorption isotherm, thermodynamics, and kinetics with corresponding model fitting were discussed, which suggested that the monolayer and chemical adsorption dominated the adsorption process. Characterization results indicated that amino and hydroxyl groups contributed electrons in the photocatalysis reaction for the reduction of Cr(VI) to Cr(III). CuS nanocrystals can enhance the surface charge and light absorbance ability of the composite, and the Cr(VI) removal was governed by electrostatic interaction and photo-induced redox reaction.

CuS-Based Nanostructures as Catalysts for Organic Pollutants Photodegradation

The direct or indirect discharge of toxic and non-biodegradable organic pollutants into water represents a huge threat that affects human health and the environment. Therefore, the treatment of wastewater, using sustainable technologies, is absolutely necessary for reusability. Photocatalysis is considered one of the most innovative advanced techniques used for pollutant removal from wastewater, due to its high efficiency, ease of process, low-cost, and the environmentally friendly secondary compounds that occur. The key of photocatalysis technology is the careful selection of catalysts, usually semiconductor materials with high absorption capacity for solar light, and conductivity for photogenerated charge carriers. Among copper sulfides, CuS (covellite), a semiconductor with different morphologies and bandgap values, is recognized as an important photocatalyst used for the removal of organic pollutants (dyes, pesticides, pharmaceutics etc.) from wastewater. This review deals with recent developments in organic pollutant photodegradation, using as catalysts various CuS nanostructures, consisting of CuS NPs, CuS QDs, and heterojunctions (CuS/ carbon-based materials, CuS/organic semiconductor, CuS/metal oxide). The effects of different synthesis parameters (Cu:S molar ratios, surfactant concentration etc.) and properties (particle size, morphology, bandgap energy, and surface properties) on the photocatalytic performance of CuS-based catalysts for the degradation of various organic pollutants are extensively discussed.