Adsorption of Rhodamine b dye onto novel Biochar: Isotherm, Kinetic, thermodynamic study and antibiofilm activity

Wastewater pollution from organic dyes has been a serious and increasing environmental problem. The present work aims to synthesize and characterize biochar (BC) from shrimp shells for application as a biosorbent in the Rhodamine B (RhB) dye removal. Central Composite Rotational Design (CCRD 22) was used to determination of the ideal condition by adsorption process and BC was characterized by X-ray Diffraction (XDR), N2 porosimetry, zero charge point (pHZCP) and Scanning Electron Microscope (SEM). The toxicity was measured by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) and 2,7 Dichlorofluorescein Diacetate (DCFH-DA) assay in 293 T, HaCat, and MDBK cell lines, and antibiofilm activity was carried out against P. aeruginosa, A. baumannii, S. epidermidis and E. coli strains. BC showed an irregular morphology (semi-cubic and plates), mesoporosity (Dp ∼ 12.3 nm), pore volume around 0.43 cm3 g−1, the surface area of the 101 m2/g and pHZCP = 7.34. The best experimental fit for the adsorption data was Freundlich isotherm (equilibrium) and pseudo second-order (PSO) (kinetic model) indication a chemisorption process with a maximum adsorption capacity of 350.55 mg g−1 with 72.34 % of RhB removal (pH = 9, T = 298 K and [BC] = 4.5 g/L). Moreover, a thermodynamic study confirmed a spontaneous process (ΔG < 0), endothermic (ΔH = 64.76 kJ mol−1) and with an increase in system randomness indicating structural alterations of the BC surface and the RhB adsorbed (ΔS > 0). Regarding the BC recycling, there was a reduction from 72.10 % (349.38 mg g−1) to 46.32 % (223.38 mg g−1) after V cycles. BC showed biocompatibility (except in the higher concentration) and important antibiofilm activity of 87.5 % (P. aeruginosa), 53.12 % (S. epidermidis), 68.93 % (A. baumannii) and 51.7 % (E. coli) to 125 µg mL−1. Therefore, it was possible to synthesize and characterize an alternative biosorbent from shrimp shell waste with high adsorption capacity, meeting the circular economy for wastewater treatment.