Construction of scheelite CaWO4 with natural diatomite for boosted photocatalytic degradation of tetracycline and doxycycline antibiotics under natural conditions

Abstract

Fabrication of efficient and recyclable catalysts with natural supporting materials is still a challenge in the field of photocatalysis. In the present work, scheelite type calcium tungstate was successfully constructed with natural diatomite via in-situ co-precipitation method for effective photocatalytic degradation of tetracycline (TC) and doxycycline (DC) antibiotics. The as-synthesized photocatalysts were characterized by SEM-EDX, TEM, BET, XRD, XRF, XPS, FTIR, UV-vis DRS, PL and EIS techniques. The morphological and physiochemical analyses confirmed the successful hybridization of CaWO4 with natural diatomite. The optical, photoluminescence and electrochemical tests confirmed that the composite material displayed narrower band gap energy, lower recombination rate and facilitated separation of photogenerated carriers. After construction of CaWO4 with the diatomite structure, the TC and DC decomposition efficiencies were found 4.70 and 2.54 times higher than that of the pristine sample, respectively. Furthermore, the composite catalyst showed superior degradation performances (91.8 % for TC and 90.7 % for DC) in the presence of hydrogen peroxide as a Fenton-agent. The enhanced photocatalytic performance was assigned to the increased specific surface area and pore volume, decreased band gap energy, limited recombination rate of photoinduced carriers, decreased charge transfer resistance as well as the abundant of hydroxyl radicals. The degradation reaction was found to be mainly driven by photogenerated holes and superoxide radicals. The CWO@DT/Vis/Fenton catalytic system exhibited good performance at nearneutral pH, also the composite catalyst was sufficiently utilized in the presence of co-existing anions. Furthermore, the photocatalytic efficiency was also tested under natural sunlight irradiation and the TC degradation remained 71.4 % after four cycles, indicating the outstanding feature of the composite catalyst in outdoor process conditions. Under these circumstances, the present work demonstrated the utilization potential of natural diatomite for effective photocatalytic remediation of antibiotic molecules under natural sunlight irradiation.