TiO2-functionalized biochar from pistachio nutshells: adsorptive removal and photocatalytic decolorization of methyl orange

Abstract

Pistachio nutshells-derived biochar (PNS-BC) was utilized as a cost-effective adsorbent for competently removing a model dye, methyl orange (MO) from wastewater. Three concentrations of TiO2; 1%, 2%, and 3% were used to decorate the biochar. Analysis of morphology, stability, and structure of the three adsorbents (PNS, PNS-BC, and the TiO2 functionalized biochar; TiO2@PNS-BC) was extensively explored using various characterization techniques. The synergistic photocatalytic-adsorptive efficiency of the three adsorbents was compared. In this regard, a Box-Behnken (BB) design-based multivariate scheme was inaugurated with the target of maximizing MO removal (%R) while using the minimum possible of chemicals and resources. The impact of five variables; %TiO2, dose of TiO2-PNS, reaction time, dye concentration, and pH on the magnitude of %R was investigated. Results show that 97.69% removal of MO could be recognized over 120 min using adsorption compared to 99.47% removal over 30 min using 3% TiO2@PNS-BC as a photocatalyst. A 3% TiO2@PNS-BC was the best catalyst (compared to 1% and 2%) with a decolorization rate constant of 0.12741 min−1, ~ 1.5 × faster compared to the decolorization of MO using adsorption alone. Adsorption of MO conformed well to Langmuir isotherm. A maximum adsorption capacity (qmax) of 142.38 mg/g was achieved. Adsorption kinetics fitted well with the pseudo-second order (PSO) model. Results obtained indicated that biochar of PNS is a promising, cost-effective, and economical adsorbent.