Synthesis of Clay Derived Nanosilicates Impregnated With Prosopis Juliflora Biochar for Removal of Selected Heavy Metals in Water

Abstract

Due to growing urbanization, population growth, and industrial activity, heavy metals are now entering water bodies at a faster pace. The current treatment methods are ineffective, and this has detrimental effects for both human health and the environment. The research reports the synthesis of clay-derived nanosilicates that has been fused with biochar from Prosopis Juliflora. The effectiveness of the synthesized materials in removing heavy metals from water was then evaluated. Elemental analysis and characterization of the nanosilicates revealed the composition of silicates at 83.6% in the extract with 20% (w/v %) NaOH as extracting media gave the best with the best result. The FTIR characterization depicted a typical structure for sodium silicates with IR bands of 1000, 1500, 1700, and 3500 cm-1 describing silicate bands. Nanosilicates with an average diameter of 85 nm that are agglomerated and round in shape were successfully synthesized, as demonstrated by the morphological analysis performed using SEM and TEM. Phase analysis with XRD displayed broadband at 2θ=30o depicting the presence of silicate nanoparticles with intense peaks from 25.26o to 65.93o which is usually related to silicate nanoparticles. The characterization of biochar biomaterial prepared through pyrolysis showed elemental composition mainly of carbon and oxygen atoms when characterized by XRF and EDX. The FTIR spectra showed O-H stretching at 3500 cm-1 and a peak at 1600 cm-1 ascribed to carboxylate (COO-1) which is consistent with bands of most biochars. The XRD pattern of Prosopis biochar material showed a rise in the background level of between 11o and 13o absorption bands which is consistent with the existence of cellulose and other related organic compounds. A narrow sharp peak seen at 30o was attributed to amorphous carbon. The SEM analysis revealed key morphological patterns of fibrous structure and pith. The biochar sample depicted uneven particles of different dimensions with vascular features filled in rolls with a comparatively uniform surface as observed in the literature for most biochars. Elemental analysis of nanocomposite material of biochar and clay silicates using EDX revealed the main composition of carbon, oxygen, silica, aluminum, and iron. The FTIR spectra revealed a broad peak at 3500 cm-1 suggesting O-H stretching, a second peak at 2350 cm-1 relating to CO2 absorption, and a peak at 1063 cm-1 denoting C-O stretching vibration. XRD phase analysis of nanocomposite showed mineral crystal existence with peaks at 19.9o, 25o, and 35o identified as phyllosilicates which means successful impregnation of silicates on carbon surfaces of biochar. The SEM images and EDX revealed high peaks of silicon, aluminum, titanium, and iron a typical composition of clay minerals. The efficiency of each synthesized substance in the elimination of heavy metals from water was evaluated using batch adsorption. Clay silicates (99.2 %), Biochar (99.5 %) and composite material (99.4 %) had very good effectiveness of removal of the selected heavy metals but biochar material had the highest efficacy level. The kinetic experiments using Langmuir and Freundlich isotherms indicated a second-order kinetic model fit with data giving a straight line and better correlation r2 correlation of coefficient of 0.999.