Abstract
Contaminants of emerging concerns (CECs) spread across a wide range of organic product compounds. As biorecalcitrants, their removal from conventional wastewater treatment systems remains a herculean task. To address this issue, heterogenous solar driven advanced oxidation process based-TiO2 and other semiconductor materials has been extensively studied for their abatement from wastewater sources. In this study, we have synthesized by hydrothermal assisted co-precipitation Ag doped ZnSnO3. Structural and morphological characterizations were performed via X-ray diffraction (XRD), Fourier transform infra-red (FTIR), N2 adsorption-desorption at 77 K by Brunauer-Emmet-Teller (BET) and Barrett, Joyner, and Halenda (BJH) methods, Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), and UV-visible absorption in Diffuse reflectance spectroscopy (UV-vis/DRS) mode. Crystallite size estimate for Ag-ZnSnO3 and undoped form was 19.4 and 29.3 nm, respectively, while respective TEM particle size estimate was 79.0 nm and 98.2 nm. BET surface area and total pore volume by BJH for Ag-ZnSnO3 were estimated with respective values of 17.2 m2/g and 0.05 cm3/g in comparison to 18.8 m2/g and 0.06 cm3/g for ZnSnO3. Derived energy band gap (Eg) values were 3.8 eV for Ag-ZnSnO3 and 4.2 eV for ZnSnO3. Photocatalytic performance of Ag-ZnSnO3 was tested towards caffeine achieving about 68% removal under (natural) unmodified pH = 6.50 and almost 100% removal at initial pH around 7.5 after 4 h irradiation. The effect of initial pH, catalyst dosage, pollutant concentration, charge scavengers, H2O2, contaminant inorganic ions (anions) as well as humic acid (HA) on the photocatalyst activity over caffeine degradation were assessed. In accordance with the probation test of the reactive species responsible for photocatalytic degradation process, a reaction mechanism was deduced.
Highlights
Caffeine overuse has been reported with side effects of irritability, DNA mutation, anxiety and tremors, and bone mass loss with risk of cardiovascular illnesses [13,14,15]
Perceived to be harmful in the long run to humans and environment due to their recalcitrant and bioaccumulative nature, research efforts towards removing contaminants of emerging concerns (CECs) prior to the end of pipe discharge in conventional wastewater treatment, which they elude by reason of their resistance to such treatment approach, has intensified [16]
The crystallite sizes of the obtained samples were 29.3 nm and 19.4 nm for ZnSnO3 and Ag-ZnSnO3, respectively (Table 1). This was derived by the Debye-Scherrer function as stated in Equation (2) using the X-ray diffraction (XRD) line broadening of the most intense peak (Figure 1a)
Summary
Global population explosion with increase demand in food production, energy and adequate healthcare system for improved social welfare has left the natural environment unbalanced [1,2]. Amongst several sources of water environmental pollution, contaminants of emerging concerns (CECs) remain alarming and issue of public concern [3,5,6,7]. These are chemicals encompassing wide range of organic products from pharmaceuticals and personal healthcare 4.0/). Caffeine (C8 H10 N4 O2 ) is an alkaloid of the methylxanthine family; a psychoactive substance example of PPCP and very often detected in municipal wastewater treatment plants (MWWTPs) and surface waters [8,9]. Perceived to be harmful in the long run to humans and environment due to their recalcitrant and bioaccumulative nature, research efforts towards removing CECs prior to the end of pipe discharge in conventional wastewater treatment, which they elude by reason of their resistance to such treatment approach, has intensified [16]
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