The massive generation of medical waste (MW) results in a series of environmental, social, and ecological problems. Pyrolysis is one such approach that has attracted more attention because of the production of value-added products with lesser environmental risk. In this study, the activated biochar (ABC600) was obtained from MW pyrolysis and activated with KOH. The adsorption mechanism of activated biochar on cationic (methylene blue) and anionic (reactive yellow) dyes were studied. The physicochemical characterization of biochar showed that increasing pyrolysis temperature and KOH activation resulted in increased surface area, a rough surface with a clear porous structure, and sufficient functional groups. MB and RYD-145 adsorption on ABC600 was more consistent with Langmuir isotherm (R² ≥ 0.996) and pseudo-second-order kinetics (R² ≥ 0.998), indicating chemisorption with monolayer characteristics. The Langmuir model fitting demonstrated that MB and RYD-145 had maximum uptake capacities of 922.2 and 343.4 mg⋅g⁻¹. The thermodynamics study of both dyes showed a positive change in enthalpy (ΔH°) and entropy (ΔS°), revealing the endothermic adsorption behavior and randomness in dye molecule arrangement on activated-biochar/solution surface. The activated biochar has excellent adsorption potential for cationic and anionic dyes; hence, it can be considered an economical and efficient adsorbent.

Nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are receiving attention because of their high toxicity compared with parent PAHs. However, the experimental data of their physicochemical properties has been limited. This study proposed the gas chromatographic retention time (GC-RT) technique as an effective alternative one to determine octanol-air partition coefficients (KOA) and sub-cooled liquid vapor pressures (PL) for 11 NPAHs, 10 OPAHs, and 19 parent PAHs. The slopes and intercepts of the linear regressions between temperature versus KOA and PL were provided and can be used to estimate KOA and PL for the 40 targeted compounds at any temperature. The internal energies of phase transfer (ΔUOA) and enthalpies of vaporization (ΔHL) for all targeted compounds were also calculated using the GC-RT technique. High-molecular-weight compounds may release or absorb higher heat energy to transform between different phases. NPAHs and OPAHs had a non-ideal solution behavior with activity in octanol (γₒcₜ) in the range of 19–53 and 18–1,078, respectively, which is larger than the unity threshold. A comparison among four groups of PAH derivatives showed that a functional group (nitro-, oxygen-, chloro-, and bromo-) in PAH derivatives increased γₒcₜ for corresponding parent PAHs by tens (mono-group) to hundreds of times (di-group). This study suggests that the GC-RT method is applicable for indirectly measuring the physicochemical properties of various groups of organic compounds.

Fluoroquinolone antibiotics (FQs) are considered to be emerging environmental contaminants that have been detected extensively in aquatic environment. It is of quite importance to explore FQs interacting with dissolved organic matter (DOM). The interactions of FQs with DOM were examined by nuclear magnetic resonance (NMR) spectroscopy, fluorescence quenching, UV–vis, Fourier transform infrared (FT-IR) spectroscopic techniques. The bindings of FQs to DOM had one single binding site and their quenching mechanisms were static, which were evaluated by the Stern-Volmer and Site-binding equations. Addition of DOM could result in micro-environmental changes of fluorophores groups in FQs. The location adjacent oxygen right of Ofloxacin (OFL) and the aromatic ring (the adjacency replaced by two nitrogen-containing groups) of Ciprofloxacin (CIP), Enrofloxacin (ENR), Norfloxacin (NOR) might be highly affected by DOM molecule. The negative enthalpy change (ΔH⁰), negative entropy change (ΔS⁰) and the positive Gibbs' energy change (ΔG⁰) figured out that the binding processes were exothermic but not thermodynamic favorable, the formation of HA-FQs complexes would be powered chiefly by the ΔS⁰. H-bonding, electrostatic effect, van der Waals force were the acting force in the binding reactions and the π-π stacking effect was the major binding force under alkaline conditions. Moreover, the protonated, deprotonated, or partially protonated state of FQs were found to have different binding capacity to DOM, and the binding reactions for FQs-HA system were suppressed as the ionic strength increased. Meanwhile, alterations of FQs conformation in the presence of DOM were evaluated by FT-IR and UV–vis spectra.

Analytical techniques used to assess the environmental risk of contamination from polycyclic aromatic hydrocarbons (PAHs) typically consider only abiotic sample parameters. Supercritical fluid extraction and sorption enthalpy experiments previously suggested slow desorption rates for PAH compounds in two coal-contaminated floodplain soils. In this study, the actual PAH availability for aerobic soil microorganisms was tested in two series of soil-slurry experiments. The experimental conditions supported microbial degradation of phenanthrene if it was weakly sorbed onto silica gel. Native coals and coal-derived particles in two soils effectively acted as very strong sorbents and prevented microbial PAH degradation. The long history of PAH exposure and degree of coal contamination apparently had no influence on the capability of the microbial soil community to overcome constraints of PAH availability. Within the context of the experimental conditions and the compounds chosen, our results confirm that coal-bound PAHs are not bioavailable and hence of low environmental concern.

Ion sorption on soil and sediment has been reported to be potentially affected by bacteria which may interact both physically and chemically with solid surfaces. However, whether and how bacteria affect the sorption of inorganic phosphate (P) on soil colloids remains poorly known. Here, we comparably investigated the P sorption on four soil colloids (three highly weathered soils including two Oxisols and one Ultisol and one weakly weathered soil Alfisol) and their complexes with Bacillus subtilis and Pseudomonas fluorescens. Batch experiments showed a notable reduction in P sorption on the colloids of highly weathered soils by the two bacteria at varying P concentrations and pHs; whereas that on the colloids of Alfisol appeared to be unaffected by the bacteria. The inhibitory effect was confirmed by both greater decline in P sorption at higher bacteria dosages and the ability of the bacteria to desorb P pre-adsorbed on the colloids. Further evidence was given by isothermal titration calorimetric experiments which revealed an alteration in enthalpy change caused by the bacteria for P sorption on Oxisol but not for that on Alfisol. The B. subtilis was more efficient in suppressing P sorption than the P. fluorescens, indicating a dependence of the inhibition on bacterium type. After association with bacteria, zeta potentials of the soil colloids decreased considerably. The decrease positively correlated with the decline in P sorption, regardless of soil and bacterium types, demonstrating that the increment in negative charges of soil colloids by bacteria probably contributed to the inhibition. In addition, scanning electron microscopic observation and the Derjaguin–Landau–Verwey–Overbeek theory prediction suggested appreciable physical and chemical interactions between the bacteria and the highly weathered soil colloids, which might be another contributor to the inhibition. These findings expand our understandings on how bacteria mobilize legacy P in soils and sediments.

Herein, activated carbon supported modified with bimetallic-platin ruthenium nano sorbent (PtRu@AC) was synthesized by a thermal decomposition process and used in the removal of methylene blue (MB) from aqueous solutions. The synthesized nano sorbents were characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS) spectroscopic techniques. The data obtained from characterization studies showed that PtRu@AC nano sorbent was highly crystalline and in a form of PtRu alloy with a monodispersed composition. The results indicated that the maximum adsorption capacity (qemax) for the removal of MB with PtRu@AC under optimum conditions was detected to be 1.788 mmol/g (569.4 mg/g). The experimental kinetic results of the study revealed that the adsorption of methylene blue was found to be more compatible with the false second-order model compared to some tested models. Calculations for thermodynamic functions including enthalpy change (ΔHo), entropy change (ΔSo), and Gibbs free energy change (ΔGo) values were performed to get an idea about the adsorption mechanism. As a result, the synthesized PtRu@AC nano adsorbent was detected as a highly effective adsorbent material in the removal of MB from aquatic mediums.

Polychlorinated biphenyls (PCBs) have been detected as prevalent environmental contaminants in water, food and biota. Previous studies in vitro have shown that a variety of sorbent materials, including carbon, can sorb PCBs; however, PCB sorbents that can be added to food or drinking water to decrease toxin bioavailability in humans and animals have not been reported. To address this problem, we have developed a broad-acting and highly effective sorbent for PCBs using montmorillonite clays reported to be safe for consumption in animals and humans. In this study, calcium montmorillonite clays were acid processed (APMs) and the interactions of six PCB congeners (PCB 77, 126, 153, 157, 154 and 155) on the surfaces of APMs were characterized. Computational models and isothermal analyses were used to derive surface capacities and affinities, delineate mechanisms and predict the thermodynamics of sorption. To confirm the safety and predict the efficacy of APMs against individual PCBs and common mixtures (Aroclors 1254 and 1260), we have also used a living organism (Hydra vulgaris) that is sensitive to toxins. APMs significantly protected hydra against the toxicity of PCBs and Aroclors. This finding was supported by studies showing tight binding; high capacity, affinity, and enthalpy; and a low therapeutic dose.

Metal-resistant bacteria can survive exposure to high metal concentrations without any negative impact on their growth. Biosorption is considered to be one of the more effective detoxification mechanisms acting in most bacteria. However, molecular-scale characterization of metal biosorption by wild metal-resistant bacteria has been limited. In this study, the Pb(II) biosorption behavior of Serratia Se1998 isolated from Pb-contaminated soil was investigated through macroscopic and microscopic techniques. A four discrete site non-electrostatic model fit the potentiometric titration data best, suggesting a distribution of phosphodiester, carboxyl, phosphoryl, and amino or hydroxyl groups on the cell surface. The presence of these functional groups was verified by the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, which also indicated that carboxyl and phosphoryl sites participated in Pb(II) binding simultaneously. The negative enthalpy (−9.11 kJ mol−1) and large positive entropy (81.52 J mol−1 K−1) of Pb(II) binding with the bacteria suggested the formation of inner-sphere complexes by an exothermic process. X-ray absorption fine structure (XAFS) analysis further indicated monodentate inner-sphere binding of Pb(II) through formation of C−O−Pb and P−O−Pb bonds. We inferred that C−O−Pb bonds formed on the flagellar surfaces, establishing a self-protective barrier against exterior metal stressors. This study has important implications for an improved understanding of metal-resistance mechanisms in wild bacteria and provides guidance for the construction of genetically engineered bacteria for remediation purposes.

The catalytic hydrolysis of carbonyl sulfide (COS) and the effect of small clusters of H2O and H2SO4 have been studied by theoretical calculations. The addition of H2SO4 could increase the enthalpy change (ΔH<0) and decrease relative energy of products (relative energy<0), resulting in hydrolysis reaction changed from an endothermic reaction to an exothermic reaction. Further, H2SO4 decreases the energy barrier by 5.25 kcal/mol, and it enhances the catalytic hydrolysis through the hydrogen transfer effect. The (COS + H2SO4-H2O) reaction has the lowest energy barrier of 29.97 kcal/mol. Although an excess addition of H2O and H2SO4 increases the energy barrier, decreases the catalytic hydrolysis, which is consistent with experimental observations. The order of the energy barriers for the three reactions from low to high are as follows: COS + H2SO4-H2O < COS + H2O + H2SO4-H2O < COS + H2O+(H2SO4)2. Kinetic simulations show that the addition of H2SO4 can increase the reaction rate constants. Consequently, adding an appropriate amount of sulfuric acid promotes the catalytic hydrolysis of COS both kinetically and thermodynamically.