Abstract
The presence of toxic, non-biodegradable and harmful organic pollutants in soils, wastewater, and atmosphere has become an indisputable, and global fact as a significant environmental problem. The heterogeneous photocatalysis, an advanced oxidation process (AOP) using semiconductor materials as catalysts, is a topic of great interest considering the possibility of the pollutants removal from water. The photocatalytic degradation of organic contaminants (i.e., dyes, pesticides, phenolic compounds) present in water using semiconductor materials depends on a number of parameters such as: the bandgap energy, phase composition, crystallinity, morphology and surface area of catalyst, electron-hole recombination rate, intensity of light, and adsorption capacity of the dye on the photocatalyst surface. One of the important constraints related to the catalyst photocatalytic efficiency is the fast recombination of the photogenerated electrons and holes. Therefore, various strategies have been involved in promoting the charge separation, including the development of heterojunction between two semiconductor materials, by tailoring the photocatalysts properties. This mini-review deals with the recent developments on dyes photodegradation using as catalysts various heterojunctions based on copper sulfide nanostructures, such as copper sulfide/metal oxide, copper sulfide/metal sulfide, copper sulfide/graphene, copper sulfide/organic semiconductors etc. The effects of different parameters, such as synthesis parameters, particle size, bandgap energy, surface area, and morphology on the photocatalytic activity of copper sulfide heterojunctions for dyes degradation is also highlighted.
Highlights
Heterogeneous photocatalysis, an advanced oxidation process, requires energy and solar energy can be a viable source, for carefully selected catalysts, meaning materials with high absorption capacity for solar light, and conductivity for photogenerated charge carriers
Copper sulfides with different morphologies, and bandgap values are recognized as important semiconducting materials with potential applications in many fields such as solar cells (Isac et al, 2011; Yan et al, 2013), photocatalysis (Cao et al, 2015; Srinivas et al, 2015; Ayodhya et al, 2016; Li et al, 2017; Wu et al, 2017), lithium-ion rechargeable batteries (Yang et al, 2018), supercapacitors (Krishnamoorthy et al, 2014), electrochemical biosensing (Liu et al, 2014), photothermal conversion (Fang et al, 2018; Rokade et al, 2018), and as materials exhibiting localized surface plasmon resonance (LSPR) absorption (Jia et al, 2017)
The lack of standards in the field of photocatalysis and photocatalytic heterojunctions make it impossible to compare the results provide by different researchers, with all these inconveniences, some indicative optimized parameters can be given: the catalyst concentration between 0.5 and 2 g/L, the dyes concentration around 10 mg/L
Summary
Heterogeneous photocatalysis, an advanced oxidation process, requires energy and solar energy can be a viable source, for carefully selected catalysts, meaning materials with high absorption capacity for solar light, and conductivity for photogenerated charge carriers. The photodegradation of MB solutions, without the assistance of H2O2 which obviously accelerate the dye degradation, was carried out to evaluate the photocatalytic activity of CuS/GO and CuS/rGO (reduced graphene oxide) based catalysts under Vis light irradiation.
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