Sustainable mesoporous graphitic activated carbon as biosorbent for efficient adsorption of acidic and basic dyes from wastewater: Equilibrium, kinetics and thermodynamic studies

Abstract

Mesoporous graphitic activated carbon (MGAC) was synthesized using inexpensive Peltophorum pterocarpum leaf as a biomass precursor by a simple and efficient method at 550 °C. As prepared MGAC was exhibited mesoporous nature, high surface area as with high adsorption capacity for removal of synthetic dyes as well as industrial effluents. The complete formation of MGAC has been characterized by different analytical techniques such as X-Ray Diffraction (XRD), Raman, Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM), Energy Dispersive X-ray Analysis (EDAX), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area analysis, Thermogravimetric Analysis (TGA) and the associated Differential Thermal Analysis (DTA). The FE-SEM and HR-TEM images relieved that the presence of an enormous amount of pores and a large specific area for the adsorption of dyes. And also, BET analysis showed 881 m2/g of surface area along with mesopores diameter of 2-6 nm respectively. The XRD and Raman data showed as prepared MGAC in graphitic nature. Further, the MGAC has exhibited good absorption capacity towards acidic dyes such as 868.28 mg/g for Acid blue 113 (AB113) and 151 mg/g for Acid blue 9 (AB9). And also, exhibited towards basic dyes such as 170.10 mg/g for Rhodamine B (RB), 221.81 mg/g for Safranin O (SO) and 272.66 mg/g for Malachite Green (MG)) respectively. Moreover, the optimum MGAC adsorbent dose was found 0.18 g, 0.03 g, 0.06 g, 0.1 g & 0.12 g for AB9, AB113, SO, RB and MG respectively. The equilibrium was attained at 180 min. for all the dyes. Additionally, adsorption of all the dyes followed the Langmuir adsorption isotherm by best fitting of equilibrium as regression coefficient of R2= 0.99, which is confirmed the monolayer coverage of dye molecules on MGAC. Furthermore, the adsorption kinetics data tracked the pseudo second order. In addition, the thermodynamic studies reveled that adsorption is spontaneous as well endothermic and might be chemisorption in nature. Finally, 0.5 g of MGAC displayed tremendous capability for the removal of mixture of synthetic dyes (each dye con. is 6 × 10−4 M) as well industrial effluents were removed with 0.1 g of MGAC. Comparative study about other adsorbents showed reasonable capacity for selected both acid and basic dyes over single MGAC adsorbent. Besides, the sustainability was exhibited with 0.03 g of MGAC through remarkable stability and reusability up to 5 cycles of run. The adsorption mechanism explained based on synergetic interactions of hydrogen bonding, π-π interactions and electrostatic interactions through effect of pH. Therefore, complete results advised that MGAC is a prominent adsorbent for efficient removal of both acidic and basic dyes as well industrial effluents present in the wastewater.