Abstract
Achieving photocatalytic carcinogenic hexavalent chromium (Cr(VI)) reduction by utilising a visible light promoted semiconductor based nanocomposite is challenging as a eco-friendly and sustainable approach. Mesoporous MCM-41 modified ZnCr Layered double hydroxide (LDH) nanocomposite was prepared by in-situ co precipitation method having great porosity, large surface area, high chemical stability and plentiful surface –OH grafting sites. These sites can be easily tailored with APTES group as amine source using a facile reflux process to design amine functionlisation ZnCr LDH/MCM-41 nanohybrid material. The structural identity, textural properties, optical response and functional groups of the as-prepared materials were systematically analysed by powder X-ray diffraction (PXRD), N2 adsorption–desorption technique, ultraviolet–visible diffuse reflectance (UV–vis DRS) and fourier-transform infrared (FTIR). It is revealed that the amine functionlisation ZnCr LDH/MCM-41 possesses enhanced visible-light absorption property in compared to ZnCr/MCM-41 nanocomposite, which was attributed to the chromophoric amino group of the organic linker. Under optimum conditions, amine functionlisation ZnCr LDH/MCM-41 exhibited 95% Cr(VI) reduction in 2 h from aqueous solution under visible-light irradiation, which was 1.2 times higher than that of unmodified ZnCr LDH/MCM-41 nanocomposite and 1.5 times superior than pure ZnCr LDH. The lowest PL intensity of amine functionlisation ZnCr LDH/MCM-41 supported the optimum photocatalytic activity. Under the explore of visible light, the presence of LMCT spectra (O2p → Cr-3dt2g and Zn 4 s) an d–d transition (Cr-3d-t2g → Cr-3 deg) in the ZnCr LDH are the key reason for excited of photoelectrons and transportation from amine functionlisation ZnCr LDH/MCM-41 to Cr(VI), accelerating the reduction process of Cr(VI). In summary, amine functionalized MCM-41 modified ZnCr LDH could be prospective photocatalyst candidate for the treatment of Cr(VI)-contained wastewater under visible light irradiation.
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