Hydrated titanium oxide nanoparticles supported on natural rice straw for Cu (II) removal from water

This study combined agricultural waste utilization with wastewater treatment and developed a novel nanocomposite adsorbent for Cu 2 + ${}^{2+}$ removal from water. Rice straw (RS) was used as the supporter of hydrated titanium oxide (HTO), which has strong affinity toward heavy metals. HTO nanoparticles were uniformly loaded onto the surface of natural rice straw through a facile sol–gel method. The characterization results show that the diameter of the RS-HTO nanoparticles was about 80 nm with SEM. The fabricated nanocomposite RS-HTO exhibited excellent structural stability under different solution pH and ionic strength. Adsorption of Cu 2 + ${}^{2+}$ increased as pH rose from 2.0 to 7.5 with 2 g/L RS-HTO in 50 mL solution (10 mg/L). Meanwhile, when initial concentration of Cu 2 + ${}^{2+}$ was 10 mg/L, the adsorptive removal efficiency was higher than 99% by RS-HTO at a pH level of 7.5. The adsorption selectivity was investigated and proved that the coexisting cation ions such as Na + ${}^{+}$ , Mg 2 + ${}^{2+}$ and Ca 2＋ led to a small decrease of Cu 2 + ${}^{2+}$ adsorption capacity. Adsorption isotherms of Cu 2 + ${}^{2+}$ onto RS-HTO fitted well with Langmuir equation, and the adsorption kinetics were best described by pseudo-second order model. The concentration of Cu 2 + ${}^{2+}$ in the simulated wastewater can be reduced to be lower than 0.2 mg/L through fixed-bed adsorption process and the exhausted RS-HTO can be easily regenerated with HCl–NaCl mixed solution.