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Utilization of environmentally friendly and effective synthesis methods to fabricate visible light responsive photocatalysts with impressive catalytic performance is desirable in photocatalytic water treatment. Herein, we employed the powerful and environmentally benign ultrasonic synthesis to hybridize hydrothermally prepared NiNb2O6 with varying amounts of RGO (5, 10 and 15 wt%) obtained via a modified Hummers' method. The samples were characterized extensively using analytical techniques such as XRD, SEM-EDX, TEM, UV-Vis DRS, PL, XPS, M-S and EIS, and subsequently employed for the degradation of doxycycline (DOX) and tetracycline hydrochloride (TC) in water under visible light exposure. The binary nanocomposites displayed enhanced activity compared to NiNb2O6, with the highest activity attained over the 10 wt% RGO sample (NiNb2O6/10 wt% RGO) which achieved 89.2% and 94.1% DOX and TC removal in 80 min, respectively. This was ascribed to improved visible light response, and charge separation and transfer. Furthermore, the influence of pH, pollutant initial concentration and photocatalyst dose was investigated. The hydroxyl radicals and holes were identified as the predominant reactive species responsible for degradation of both DOX and TC. Finally, a feasible charge transfer pathway was proposed to explain the formation of the reactive species and GC-MS analysis was employed to track the degradation route of DOX. This work presents a simple and effective route for coupling RGO and NiNb2O6 nanoparticles for antibiotic pollution abatement which is currently a major environmental concern. [ABSTRACT FROM AUTHOR]

The exploitation of visible light active photocatalysts for the removal of various pollutants has been given tremendous consideration in water and wastewater treatment. Herein, a novel In2S3/CeO2 n–n type heterojunction photocatalyst was successfully synthesized by a two-step method involving hydrothermal synthesis and subsequent ultrasonic treatment to couple In2S3 with CeO2 (5, 10 and 15 wt%). The as-synthesized samples were characterized extensively using analytical techniques such as XRD, UV-vis-DRS, SEM-EDX, TEM, BET, PL, EIS and XPS to examine the chemical composition, phase structure, morphology and photo-chemical characteristics of the materials. Subsequently, the In2S3/CeO2 nanostructures were employed in the degradation of oxytetracycline (OTC) (10 mg L−1) and reduction of Cr(VI) (50 mg L−1) in aqueous solutions, upon exposure to visible light. Under optimised experimental conditions, the nanocomposite constituting 10 wt% CeO2 (In2S3/10 wt% CeO2) showed the highest activity, reaching 87.9% OTC degradation and 97.5% Cr(VI) reduction after 60 min and 40 min of visible light irradiation, respectively. The nature and contribution of active species in the photocatalytic process were revealed through radical scavenging studies. Finally, a plausible band structure, charge separation and transfer mechanism were crafted to illustrate the synergy between In2S3 and CeO2 which led to improved degradation kinetics. This work demonstrated a simple route for improving the visible light-mediated activity of In2S3 by coupling with CeO2 and the potential versatility of the composite material for the removal of both organic and inorganic pollutants from water. [ABSTRACT FROM AUTHOR]