AUTHOR=Al-Labadi Ibrahim G. , Shemy Marwa H. , Ghidan Alaa Y. , Allam Ahmed A. , Kálmán Horváth M. , Ajarem Jamaan S. , Luo Jianmin , Wang Chuanyi , Abukhadra Mostafa R. 

TITLE=Insight into the effects of H2SO4 and HNO3 acidification processes on the properties of coal as an enhanced adsorbent for ciprofloxacin residuals: Steric and energetic studies

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2023.1130682

DOI=10.3389/fchem.2023.1130682

ISSN=2296-2646

ABSTRACT=Sub-bituminous natural coal sample (R.C) was treated with sulphuric acid (S.C) and nitric acid (N.C) as modified products and enhanced adsorbents for the residual of ciprofloxacin antibiotic from water as pharmaceutical residuals. The characterization studied demonstrates enhancement in the surface area and the incorporation of new active oxygenated, sulfur-bearing, and nitrogen-bearing chemical groups into the structure of the coal samples. This was reflected in the adsorption capacities that enhanced from 164.08 mg/g (R.C) to 489.2 mg/g and 518.5 mg/g for N.C and S.C, respectively. The impact of the acid modification processes was evaluated based on the energetic and steric properties of their adsorption systems considering the parameters of the advanced monolayer equilibrium model with one energy site. The determined occupied active sites density of R.C (46.32-61.44 mg/g), N.C (168.7-364.9 mg/g), and S.C (159.2-249.9 mg/g) reflect an increase in the quantities of the active center after the acid treatment processes, especially with HNO3. The higher efficiencies of the active sites of S.C to adsorb more CFX molecules (n = 2.08 to 2.31) than N.C (n = 1.41 to 2.16) illustrate its higher adsorption capacity. The energetic investigation [adsorption (˂40 kJ/mol) and Gaussian (˂8 kJ/mol) energies] suggested adsorption of CFX by N.C and S.C mainly by physical processes such as van der Waals forces, hydrogen bonding, dipole bonding, π–π interactions. Moreover, the determined thermodynamic functions including entropy, internal energy, and free enthalpy reflect the spontaneous and endothermic uptake of CFX on the surfaces of N.C and S.C