Template-free conversion of rice husk silica into nano-zeolite X and its application in adsorption of heavy metal ions

Abstract

Template-free synthesis of nano-zeolite X at a high crystallization temperature and shorter time is attempted using rice husk ash silica, a low-cost and sustainable silica source, and the potential of the adsorbent for heavy metals is investigated. Rice husk ash silica and zeolites were characterized using XRF, XRD, SEM, FTIR, 29Si solid-state NMR, and N2 adsorption/desorption to determine the elemental composition, mineralogy, morphology, functional and framework structures, respectively. Static hydrothermal treatment (HT) at 100 °C for 6 h was established as the optimum synthesis condition for nano-zeolite X exhibiting particle size ~ 72 nm; pyramidal octahedral morphology with specific surface area and external surface area of 433 and 43 m2/g, respectively. The maximum adsorption capacity of NZX (qm) for Cu2+ and Ni2+ was 60.24 mg/g and 36.90 mg/g, respectively. The adsorption is spontaneous and thermodynamically feasible; it can best be described by the Langmuir isotherm and pseudo-second-order kinetic model.