Synthesis of piliostigma reticulatum decorated TiO2 based composite and its application towards Cr(VI) adsorption and bromophenol blue degradation: Nonlinear kinetics, equilibrium modelling and optimisation photocatalytic parameters

In this study, the use of wild bio-waste piliostigma fruits as an alternative precursor for titanium dioxide doped carbon and a simple synthesis method for the preparation of novel eco-friendly TiO2-AC (AC stand for activated carbon) based composites following two routes (TiO2-AC1 and TiO2-AC2) were proposed. The structure, morphology, chemical composition, surface area, light absorption and crystalline phase of the composites were systematically characterised using Fourier transform infrared spectroscopy, scanning electron microscopy, BET analysis, Raman spectroscopy, X-ray fluorescence spectrophotometry fundamental parameters and X-ray Diffraction. The adsorptive capability of the composites were tested towards Cr(VI) elimination and the Box Behnken Design (BBD) with a desirability function was implemented to optimise the photocatalytic parameters towards Bromophenol Blue (BPB) dye degradation. As a result, high adsorption quantity of 3.46 mg/g (TiO2-AC1) and 3.49 mg/g (TiO2-AC2) were obtained at optimum adsorption parameters. Kinetics study showed a good nonlinear fit with pseudo second order and isotherms modelling are well described by Sips and MarczewskiJaroniec models. The degradation efficiency of bromophenol blue (BPB) by the TiO2-AC2 composite reached 100%, however 57.90% only was recorded for TiO2 at about 180 min of UV irradiation. The kinetics of degradation followed pseudo first order model and the optimal conditions provided by the response surface methodology (RSM) was pH 3, photocatalyst dose 300 mg/L and salt interference of 10 mg/L. This trend proposed a mechanism for preparation of biomass-based TiO2-AC composite and revealed that the use of RSM optimisation process contributes to save time and ensure proper materials handling through degradation as a sustainable water treatment technology.