Synthesis and Characterization of Carbon and Carbon-Nitrogen Doped Black TiO(2) Nanomaterials and Their Application in Sonophotocatalytic Remediation of Treated Agro-Industrial Wastewater

The conventional open ponding system employed for palm oil mill agro-effluent (POME) treatment fails to lower the levels of organic pollutants to the mandatory standard discharge limits. In this work, carbon doped black TiO(2) (CB-TiO(2)) and carbon-nitrogen co-doped black TiO(2) (CNB-TiO(2)) were synthesized via glycerol assisted sol-gel techniques and employed for the remediation of treated palm oil mill effluent (TPOME). Both the samples were anatase phase, with a crystallite size of 11.09–22.18 nm, lower bandgap of 2.06–2.63 eV, superior visible light absorption ability, and a high surface area of 239.99–347.26 m(2)/g. The performance of CNB-TiO(2) was higher (51.48%) compared to only (45.72%) CB-TiO(2). Thus, the CNB-TiO(2) is employed in sonophotocatalytic reactions. Sonophotocatalytic process based on CNB-TiO(2), assisted by hydrogen peroxide (H(2)O(2)), and operated at an ultrasonication (US) frequency of 30 kHz and 40 W power under visible light irradiation proved to be the most efficient for chemical oxygen demand (COD) removal. More than 90% of COD was removed within 60 min of sonophotocatalytic reaction, producing the effluent with the COD concentration well below the stipulated permissible limit of 50 mg/L. The electrical energy required per order of magnitude was estimated to be only 177.59 kWh/m(3), indicating extreme viability of the proposed process for the remediation of TPOME.