H3PO4-modified Lagerstroemia speciosa seed hull biochar for toxic Cr(VI) removal: isotherm, kinetics, and thermodynamic study

The novelty of the present work was to prepare biochar by utilizing waste biomass (Lagerstroemia speciosa) seed hull (LSSH) through pyrolysis process followed by chemical modification with H3PO4. This chemically modified biochar was employed as an adsorbent for toxic Cr(VI) removal in batch adsorption process due to its high surface area (246.23 m(2)g(-1)) and low pore size (2.36 nm). Thermal stability of LSSH was examined in a thermogravimetric analyzer from 20 to 700 degrees C in an inert environment (N-2 flow rate = 100 ml/min). Proximate analysis of LSSH revealed lower moisture content (3.7%) and higher volatile matter (74.1%), whereas elemental analysis results revealed significant increase in carbon content after pyrolysis (38.94% to 45.85%). Higher heating (HHV) value of LSSH and LSSB was obtained to be 17.57 (MJ Kg(-1)) and 18.06 (MJ Kg(-1)) respectively. The maximum amount of Cr (VI) removal was obtained to be 99.97% at optimized operating condition of pH = 2, adsorbent dosage = 2 g L-1, chromium concentration = 50 mg L-1, and temperature = 303 K. The value of maximum adsorption capacity Q(m) based on Langmuir model, enthalpy change ( increment H degrees), entropy change ( increment S degrees), and standard free-energy change ( increment G degrees), was obtained as 41.92 mg g(-1), 174.28 kJ mol(-1), 0.62 kJ mol(-1) K-1, and 15.4 kJ mol(-1), respectively at 303 K. Adsorption was noticed to be endothermic followed Langmuir isotherms (R-2 = 0.9996) with pseudo-second-order kinetics (R-2 = 0.998). The comparative assessment of adsorption capacity along with other biosorbents suggests that CLSSB can be utilized as an effective adsorbent for toxic Cr(VI) removal as well as other pollutants-containing wastewater.

Automated summary

This study prepared chemically modified biochar from waste biomass (Lagerstroemia speciosa) seed hull and utilized it as an adsorbent for removing toxic Cr(VI) in batch adsorption process. The chemically modified biochar exhibited high surface area and low pore size, making it an effective adsorbent for Cr(VI) removal.