ZnO nanoparticles loaded rice husk biochar as an effective adsorbent for removing reactive red 24 from aqueous solution

In this study, rice husk biochar (RHB) and ZnO nanoparticles loaded rice husk biochar (RHB-ZnO-3 served to adsorb Reactive red 24 (RR24) in an aqueous solution. Effects of the ZnO nanoparticles loading ratio, solution pH, contact time, and initial RR24 concentration were evaluated utilizing detailed batch adsorption conditions. Isotherm and kinetic models helped to analyze the RR24 adsorption. Shown here is that the ratio of 3% (w/w) ZnO nanoparticles to RHB proved to be the best for fabricating highly effective modified rice husk biochar. In this scenario, the BET surface area of RHB-ZnO-3 was 13.84 m2/g, more than triple the original RHB (4.01 m2/g). Experimental results strongly suggest that RR24 highest adsorption capacities onto RHB-ZnO-3 and RHB were 174.91 mg/g and 88.51 mg/g, respectively. The best pH contact time and adsorbent rate for RR24 removal were 3, 60 min and 1.0 g/L, respectively. RR24 adsorption onto RHB and RHB-ZnO-3 were well described by Pseudo-second order kinetic and Langmuir isotherm models. Adsorption capacities of RHB and RHB-ZnO-3 did not diminish significantly after five cycles of adsorption-desorption. RHB and RHB-ZnO-3 could remove: firstly, more than half of the color and COD (50% color, 52.5% COD); and secondly, most of the turbidity (82.8%) from real textile wastewater. Electrostatic attraction, π-π interaction and pore filling were the main adsorption mechanisms of RR24 onto RHB and RHB-ZnO-3.