Insight into the sunlight-mediated photodegradation of active pharmaceuticals using ZnO-doped TiO2/Carbon nanocomposite derived from leather waste

Treatment of pharmaceutical wastewater is gaining importance due to health risks. In this study, carbon sourced from vegetable-tanned leather waste was utilized to develop an effective photocatalyst. ZnO incorporated TiO 2 /carbon nanocomposites were synthesized via the sol–gel route by systematically changing the TiO 2 :ZnO mass ratio. The nanocomposites exhibited a reduction in band gap energy values and particle size as ZnO content increased. The photocatalytic performance of the synthesized materials was tested for degrading sulfasalazine (SUZ) and losartan potassium (LP) under visible light and sunlight conditions. The ZnO@TiO 2 /carbon (with a 1:0.075 mass ratio of TiO 2 :ZnO) nanocomposite with a band gap energy of 3.23 eV demonstrated maximum degradation efficiencies of 97% and 96% for SUZ and LP, respectively, under sunlight illumination within 120 min. The photocatalytic degradation of SUZ was studied using radical scavengers and EPR spin-trap experiments. The findings indicate that superoxide (O 2 ⋅− ), holes from valence band (h vb + ) and adsorbed hydroxyl radicals ( ⋅ OH ads ) are the primary reactive species involved in the degradation of SUZ. Catalyst reuse was demonstrated up to three cycles. The photocatalytic performance was further evaluated in a synthetic wastewater matrix containing representative inorganic ions and natural organic matter, where the CTZ5 nanocomposite maintained appreciable degradation efficiency. ESI/MS based mechanistic studies identified 4-nitro- N -(2-pyridinyl)benzenesulfonamide and sulfapyridine as key intermediates. These findings highlight the nanocomposite’s strong potential for pharmaceutical wastewater treatment, thus contributing to environmental sustainability.