Adsorptive removal of anthraquinone dye from wastewater using silica-nitrogen reformed eucalyptus bark biochar: Parametric optimization, isotherm and kinetic studies

Abstract

BackgroundDye sequestration from textile wastewater is required prior to discharge because of environmental concerns and the potential risk posed by colored contaminants. MethodsHerein, a novel composite adsorbent of biochar derived from eucalyptus bark and 3-aminopropyl triethoxysilane (TESPA, as source of silica) and diethylene triamine (DIEN, as source of nitrogen) was synthesized via impregnation method. The prepared adsorbents were characterized by scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, N2 adsorption-desorption and pH at point of zero charge (pHpzc) analyses. The optimal TESPA: DIEN molar ratio for the silica-nitrogen doped eucalyptus bark biochar (Si-N@EBB) composite to adsorb acid blue 25 (AB25) dye was 2:1. The independent process parameters (contact duration, adsorbent dosage, pH and initial AB25 concentration) influencing the AB25 adsorption by Si-N@EBB2:1 were optimized by Box-Behnken design in response surface methodology at temperature of 26± 2 °C. The obtained experimental data were analyzed by the Langmuir, Freundlich and Temkin isotherms. Kinetic data obtained at various AB25 concentrations were evaluated using pseudo-first-order (PFO), pseudo-second-order (PSO) and intraparticle diffusion equations. Significant FindingsPredicted values of removal efficiency were found to be in agreement with the experimental values obtained (R2 = 0.9823; Adj − R2 = 0.9646). Optimization findings revealed that maximum removal efficiency of 96.03± 2.57 % was achieved at the optimum conditions of 21.01 mg L−1 initial AB25 concentration, 3.91 dye solution pH, 0.913 g L−1 adsorbent dosage and 117.2 min contact duration. The equilibrium adsorption data fitted well to the Langmuir isotherm with a monolayer uptake capacity found to be 197.4 mg g−1. PSO model suited the kinetic data well, indicating the dominance of chemisorption mechanism.