Synthesis and physicochemical characterization of a ZnO-Chitosan hybrid-biocomposite used as an environmentally friendly photocatalyst under UV-A and visible light irradiations

Physicochemical and Photocatalytic Properties under Visible Light of ZnO-Bentonite/Chitosan Hybrid-Biocompositefor Water Remediation

“…These processes are based on the insitu generation of highly reactive transitory species (i.e., HO • , O 2 •− , e − ) for refractory organic compounds’ mineralization [ 4 ]. Among the AOPs, heterogeneous photocatalysis has demonstrated high efficiency in degrading a large number of ambiguous refractory organics into readily biodegradable compounds [ 1 , 5 , 6 ]. The heterogeneous photocatalyticmechanism relieson the absorption of photons with energy able to excite an electron in valence band (VB) to conduction band (CB), thus generating electron/hole pairs with reductive/oxidative capacity (Equation (1)).…”

“…The holes can react with adsorbed water to form hydroxyl radicals (HO • ) (Equations (3) and (4)) while the electrons react with the adsorbed oxygen to give superoxide radicals O 2 •− (Equation (5)). Among the various used photocatalysts [ 7 , 8 , 9 ], ZnO pure or mixed with other materials has attracted special attention due to its good physicochemical, photocatalytic, antibacterial, and antifungal properties, its non-toxicity, its facile and low-cost production, and so forth [ 5 , 7 , 10 , 11 , 12 , 13 , 14 ]. However, like various metal oxide semiconductors, the photocatalytic effectiveness of ZnO is limited to the UV region (Band gap energy of ZnO= 3.30–3.32 eV [ 9 ]).…”

“…Furthermore, potential recycling of pure ZnO nanoparticles is very difficult and a significant amount of material is lost during the recovery process. In order to extend the photocatalytic effectiveness of ZnO to the visible domain, several experimental approaches have been explored including doping with metals and/or non-metals, dye sensitization, and mixing ZnO with other metal oxides [ 5 , 15 , 16 , 17 ].Natural materials such as chitosan and bentonite have retained special interest of researchers. Chitosan, which is a biopolymer, exhibits excellent adsorptive properties towards dyes and heavy metals [ 18 , 19 , 20 , 21 , 22 ] because of the presence of amino (-NH 2 ) and hydroxyl (-OH) groups which act as adsorption sites.…”

“…It is often used as an adsorbent for azo-dyes [ 26 ]. Many published works reported on the use of clay/chitosan and ZnO/chitosan composites as adsorbents or photocatalysts in removing dyes [ 5 , 13 , 24 , 25 , 27 , 28 ]. Fatimah et al [ 13 ] reported that the insertion of ZnO in monmorillonite matrix improved the band gap energy and enhanced the rate of photooxidation of methylene blue.In a previous investigation, Aadnan et al [ 5 ] indicated that the photocatalytic performance under visible light was significantly improved by adding 7 wt% of ZnO to the chitosan biomaterial.…”

“…Many published works reported on the use of clay/chitosan and ZnO/chitosan composites as adsorbents or photocatalysts in removing dyes [ 5 , 13 , 24 , 25 , 27 , 28 ]. Fatimah et al [ 13 ] reported that the insertion of ZnO in monmorillonite matrix improved the band gap energy and enhanced the rate of photooxidation of methylene blue.In a previous investigation, Aadnan et al [ 5 ] indicated that the photocatalytic performance under visible light was significantly improved by adding 7 wt% of ZnO to the chitosan biomaterial. Therefore, the challenge we are facing isto extend the photocatalytic activity of ZnO to the visible domain by using eco-friendly materials while improving the thermal stability of the synthesized hybrid-biocomposite.…”