Comparison the visible photocatalytic activity and kinetic performance of amino acids (non-metal doped) TiO2 for degradation of colored wastewater effluent

Abstract

Different types of amino acids as sources of carbon, nitrogen and sulfur were doped on TiO2 lattice to study the photocatalytic activity of three synthesized photocatalysts for dye removal under visible light. The phase composition, functional groups, morphology, optical properties, band gap energy and recombination rate of nanostructures were studied by X-ray diffraction (XRD), fourier transform infrared (FT-IR), field emission scanning electron microscopy with Energy Dispersive X-Ray Spectroscopy (FESEM/EDX), diffuse reflectance spectra (DRS) and photoluminescence spectroscopy (PL). These analysis verified the successful synthesis of the catalysts and showed the type of catalyst significantly affected PL analysis as l-Arginine-TiO2 (C,N co-doped TiO2) had lower recombination rate and PL intensity compared to l-Proline-TiO2 (C,N co-doped TiO2) and l-Methionine-TiO2 (C,N,S tri-doped TiO2). The firs-order kinetic model described the photodegradation of methyl orange (MO) and direct red 16 (DR16) and the rate constant for DR16 photocatalytic removal using l-Arginine (1 wt %)-TiO2 was 2.9 and 4.3 times higher compared to those of l-Methionine (1.5 wt %.)-TiO2 and l-Proline (2 wt %.)-TiO2 respectively. The effect of five processing variables and their optimum values were determined using central composite design (CCD). The result confirmed that decreasing pollutant concentration and pH and increasing catalyst concentration, irradiation time and light intensity improved the removal efficiency. The catalyst showed reusable and stable structure as 93% and 84% of DR16 and MO removed after four times of reusing.