An Eco-Friendly Modification of a Walnut Shell Biosorbent for Increased Efficiency in Wastewater Treatment

Abstract

Herein, we report the performance of some low-cost biosorbents developed by environment-friendly modification of walnut shells. Two types of biosorbents were prepared by ecological modification of walnut shell surfaces: (1) biosorbents obtained by hot water treatment (WSH2O) and (2) biosorbents produced by mercerization (WSNaOH). Different techniques were used to evaluate the morphological, elemental, and structural modification of the biosorbents, by comparison with raw materials. These characterization techniques involved scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis, and Fourier-transform infrared spectroscopy (FTIR). The biosorbents were employed for the removal of methylene blue (MB) and crystal violet (CV) cationic dyes (as model organic pollutants) from aqueous solutions. The kinetic adsorption data mainly followed the pseudo-first-order model. The maximum adsorption capacities of the produced biosorbents ranged from 102 to 110 mg/g and were observed at 330 K. Equilibrium data for adsorption were fitted to Langmuir and Freundlich isotherm models. The calculated values of thermodynamic parameters suggested that the investigated adsorption processes were exergonic (ΔG < 0) and exothermic (ΔH < 0). In addition, a possible valorization of the cost-effective and eco-friendly spent biosorbents was tested by performing secondary adsorption of the anionic dyes.

Adsorption of Brilliant Green Dye onto a Mercerized Biosorbent: Kinetic, Thermodynamic, and Molecular Docking Studies

“…Along with the rough texture of the PS sample, the presence of irregularly shaped impurities was noticed. These have been assigned mainly to the crushing and grinding process of pistachio shells, given that similar outcomes were also observed for walnut shells subjected to this process [ 26 ]. By comparison with the raw PS sample, the SEM image of PS NaOH ( Figure 1 b) reveals the ability of the NaOH to remove the solid impurities from the biosorbent surface.…”

“…Assessing the principal thermodynamic parameters (such as Gibbs free energy, enthalpy, and entropy) provides useful information regarding the energetic changes that occur during the adsorption [ 26 , 57 , 58 , 59 , 60 , 61 ]. In order to ascertain these thermodynamic parameters, it is necessary to take into consideration the adsorption equilibrium constants at a minimum of two distinct levels of temperature (e.g., 300 and 330 K).…”

“…In this study, the adsorption equilibrium constant ( K ad ) and consequently the thermodynamic parameters were estimated on the basis of two approaches. In the first approach, the adsorption equilibrium constant ( K ad ) was approximated assuming the Langmuir equilibrium parameter K L , which was converted from the (L/mg) unit to the (L/mol) unit according to Equation (1) [ 26 ]: where M w (g/mol) is the molecular weight of the pollutant subjected to adsorption (i.e., BG dye). Afterward, the dimensionless adsorption equilibrium constant ( K ad ) was estimated in conformity with Equation (2) [ 26 , 58 ]: where represents the activity coefficient ascertained on the basis of the ionic strength [ 36 , 58 , 60 ] and C ref denotes the molar concentration of the reference state.…”

“…In addition, for the adsorption process of BG to become economically feasible, researchers have focused on biodegradable, renewable, sustainable, easily available, and low-cost adsorbents, such as guava seeds [ 5 ], banana peels [ 7 ], kaolin [ 10 ], bagasse fly ash [ 12 ], sawdust [ 13 ], rice straw [ 15 ], medlar nucleus [ 17 ], Saklıkent mud [ 18 ], cashew nut shell [ 24 ], or acorn-based [ 25 ] materials. The adsorption technique has also been shown to be remarkable in the removal of other dye pollutants from aqueous solutions [ 4 , 8 , 26 , 27 , 28 ]. For example, environmentally friendly modifications to lignocellulosic materials such as walnut shells resulted in improved adsorption capabilities of two other cationic dyes with expanded medicinal applications (crystal violet and methylene blue) [ 26 ].…”

“…The adsorption technique has also been shown to be remarkable in the removal of other dye pollutants from aqueous solutions [ 4 , 8 , 26 , 27 , 28 ]. For example, environmentally friendly modifications to lignocellulosic materials such as walnut shells resulted in improved adsorption capabilities of two other cationic dyes with expanded medicinal applications (crystal violet and methylene blue) [ 26 ]. Furthermore, lignin-based magnetic biochar demonstrated significant Congo red removal efficiency in simulated wastewater [ 27 ], as well as excellent selective adsorption capability for methylene blue in binary, ternary, and quaternary dye systems [ 28 ].…”