Sorption of organic compounds by pyrolyzed humic acids

Three-birds-with-one-stone: An eco-friendly and renewable humic acid-derived material application strategy for macrolide antibiotic detection and multifunctional composite film preparation

This research proposes a simple and novel strategy for the green detection of antibiotics along with the reduction of microplastic and humic acid (HA) hazards. The entire process is based on a single-step solvent-sieving method to separate HA into insoluble (IHA) and soluble (SHA) components, subsequently recombining and designing the application according to the original characteristics of selected fractions in accordance with the zero-waste principle. IHA was applied as a dispersive solid phase extraction (DSPE) sorbent without chemical modification for the enrichment of trace MACs in complex biological matrices. The recovery of MACs was 74.06-100.84 % in the range of 2.5-1000 μg∙kg-1. Furthermore, SHA could be combined with biodegradable polyvinyl alcohol (PVA) to prepare multifunctional composite films. SHA endows the PVA film with favorable mechanical properties, excellent UV shielding as well as oxidation resistance performance. Compared with pure PVA, the tensile strength, toughness, antioxidant and UV-protection properties were increased to 157.3 Mpa, 258.6 MJ·m-3, 78.6 % and 60 % respectively. This study achieved a green and economically valuable utilization of all components of waste HA, introduced a novel approach for monitoring and controlling harmful substances and reducing white pollution. This has significant implications for promoting sustainable development and recovering valuable resources.

Role of biochar pyrolysis temperature on intracellular and extracellular biodegradation of biochar-adsorbed organic compounds

Immobilizing organic pollutants by adsorption of biochar in farmland soil is a cost-effective remediation method for contaminated soil. As the adsorption capacity of biochar is limited, biodegradation of biochar-adsorbed organic pollutants was a potential way to regenerate biochars and maintain the adsorption performance of biochars to lower the cost. It could be affected by the biochar pyrolysis temperature, but was not evaluated yet. In this study, biodegradation of adsorbed phenanthrene on a series of biochars with pyrolysis temperatures from 150 to 700 °C by Sphingobium yanoikuyae B1 was investigated using batch experiments of biodegradation kinetics at 30 °C, to explore the role of biochar pyrolysis temperature on biodegradation of biochar-adsorbed organic compounds. It was observed that 37.5-47.9% of adsorbed phenanthrene on moderate temperature-pyrolyzed biochars produced at 400 and 500 °C were biodegraded, less than that on high temperature-pyrolyzed biochars produced at ≥600 °C (48.8-60.8%) and low temperature-pyrolyzed biochars produced at ≤300 °C (63.4-92.5%). Phenanthrene adsorbed largely on the low temperature-pyrolyzed biochars by partition mechanism and thus is easily desorbed to water for a dominated intracellular biodegradation. On the high temperature-pyrolyzed biochars, phenanthrene is adsorbed largely by pore-filling mechanism and thus less desorbed to water for intracellular biodegradation. However, high temperature-pyrolyzed biochars can promote microbes to produce siderophore, H2O2 and thus release extracellular •OH for a dominated degradation of adsorbed phenanthrene by Fenton-like reaction. With the increase of biochar pyrolysis temperature, desorption and consequently the intracellular biodegradation of adsorbed phenanthrene on biochars decreased, while the secretion of siderophore and H2O2 by microbes on biochars increased to produce more extracellular •OH for degradation by Fenton-like reaction. The results could provide deep insights into the role of biochar pyrolysis temperature on biodegradation of biochar-adsorbed organic compounds, and optimize the selection of biochar with higher adsorption performance and easier regeneration for soil remediation.

Linear adsorption of organic compounds on mesoporous activated carbon in bi-solute system

Knowledge of organic compounds adsorption by adsorbents is essential for evaluating the environmental fates of organic compounds and removing them from the environment. Linear adsorption, as a supplement to the traditionally nonlinear adsorption, was previously proposed for the linear sorption of organic compounds on the mesoporous surface of carbon nanotubes (CNTs) in multi-solute system. However, CNTs are not the ideal adsorbent to verify the linear adsorption mechanism, because of their partition-like phase components such as mobile graphene layers that could be responsible for the linear sorption through linear partition mechanism instead, and thus the linear adsorption theory was argued. In this study, therefore, mesoporous activated carbon (MAC), widely accepted as the model free of partition phase components, was selected as an adsorbent to investigate the adsorption of typical organic compounds in the bi-solute system for verifying whether the linear adsorption phenomenon existed or not. The isotherm of nitrobenzene on MAC was changed from nonlinear to linear with 4-nitrophenol up to 1400 mg/L, and the linear isotherm slope decreased more as 4-nitrophenol concentration increased until 4000 mg/L. It agreed with the characteristics of adsorption (i.e., competition) but not partition (i.e., noncompetition), confirming the existence of linear adsorption. The isotherm linearity was attributed to the reduction of adsorption interactions by displacement and multilayer adsorption. Moreover, linear adsorption of apolar compounds on MAC could occur with apolar or polar competitors, while for polar compounds, linear adsorption could occur with only polar competitors. The observed linear sorption and the competition of organic compounds in the bi-solute system on MAC free of partition phase components verified that the linear adsorption existed, which gives a new insight into the adsorption theory for organic compounds. The results could provide better fundamental theory of adsorption for improving the accuracy of environmental risk assessment of organic pollution and enhancing the efficiency of organic pollution control in the environment.

Elucidation of aniline adsorption-desorption mechanism on various organo-mineral complexes

Complexes formed by organic matter and clay minerals, which are active components of soil systems, play an important role in the migration and transformation of pollutants in nature. In this study, humic-acid-montmorillonite (HA-MT) and humic-acid-kaolin (HA-KL) complexes were prepared, and their structures before and after the adsorption of aniline were analyzed. The aniline adsorption-desorption characteristics of complexes with different clay minerals and varying HA contents were explored using the static adsorption-desorption equilibrium method. Compared with the pristine clay minerals, the flaky and porous structure of the complexes and the aromaticity were enhanced. The adsorption of aniline on the different clay mineral complexes was nonlinear, and the adsorption capacity increased with increasing HA content. Additionally, the adsorption capacity of HA-MT was higher than that of HA-KL. After adsorption, the specific surface area of the complexes decreased, the surfaces became more complicated, and the aromaticity decreased because aniline is primarily adsorption onto the complexes via aromatic rings. Aniline was adsorbed onto the complexes via spontaneous exothermic physical adsorption. The amount of aniline desorbed from the complexes increased with increasing HA content, and a lag in desorption was observed, with a greater lag for HA-KL than for HA-MT.

Ultrahigh sorption of sulfamethoxazole by potassium hydroxide-modified biochars derived from bean-worm skin waste

Food processing of bean worm generates copious amount of skin as solid waste posing a serious environmental concern. The present study utilized bean worm skin (BWS) waste to produce KOH-modified biochars (KBWS-BCs) for the removal of sulfamethoxazole (SMX) from aqueous solution for the first time. Characterization of KBWS-BCs was systematically investigated via multiple instrumental analysis techniques. The sorption performance of KBWS-BCs as a function of solution pH, reaction time, initial SMX concentration, and reaction temperature was investigated using batch experiments. The classic kinetics and isotherm models were employed to fit the sorption data. KBWS-BCs exhibited large surface areas (3331-4742 m² g^-1) and ultrahigh sorption performance for SMX (maximum adsorption capacities of 909-2000 mg g^-1), which were comparable to those of other modified biochars and even those of well-designed materials. Thermodynamic study indicated that the sorption of SMX on KBWS-BCs was a spontaneous (△G° < 0) and exothermic (△H° < 0) process. Mechanism analysis showed that both chemisorption and physisorption were responsible for the adsorption of SMX by KBWS-BCs. Overall, recycling BWS for preparation of high-performance biochars can be a "win-win" strategy for both disposal of BWS and removal of SMX from wastewater.

Adsorption of soil organic matter by gel-like ferrihydrite and dense ferrihydrite

Soil is the largest terrestrial carbon pool, and adsorption of soil organic matter (SOM) by ferrihydrite is an essential geochemical process for preservation of organic carbon in soil. Freshly formed gel-like ferrihydrite and seasonally dried dense ferrihydrite are two typical morphologies of ferrihydrite in soil. However, the differences in SOM adsorption by gel-like ferrihydrite and dense ferrihydrite and the underlying mechanisms are unknown. In this study, adsorption of eight SOM or SOM-like compounds by gel-like ferrihydrite and dense ferrihydrite were compared. It was observed that the adsorption capacity of SOM by gel-like ferrihydrite (e.g., 304 mg C/g) was two orders of magnitude higher than that by dense ferrihydrite (e.g., 3.44 mg C/g). SOM adsorbed by the nanosized gel-like ferrihydrite could be mainly attributed to the heteroaggregation, confirmed by not only the TEM images but also the positive linear correlation between adsorption capacity and molecular weight of SOM. However, SOM adsorbed by the microsized dense ferrihydrite should be attributed to the pore-filling adsorption with molecular sieve effects, confirmed by the negative linear correlation between adsorption capacity and molecular weight of SOM. The obtained results could provide a new insight to understand the preservation of organic carbon by ferrihydrite in soil.

Enhanced SO2 Absorption Capacity of Sodium Citrate Using Sodium Humate

A novel method of improving the SO2 absorption performance of sodium citrate (Ci-Na) using sodium humate (HA–Na) as an additive was put forward. The influence of different Ci-Na concentration, inlet SO2 concentration and gas flow rate on desulfurization performance were studied. The synergistic mechanism of SO2 absorption by HA–Na and Ci-Na was also analyzed. The consequence shows that the efficiency of SO2 absorption by Ci-Na is above 90% and the desulfurization time added with the Ci-Na concentration rising from 0.01 to 0.1 mol/L. Both the desulfurization efficiency and time may increase with the adding of HA–Na quality in Ci-Na solution. Due to adding HA–Na, the desulfurization efficiency of Ci-Na increased from 90% to 99% and the desulfurization time increased from 40 to 55 min. Under the optimum conditions, the desulfurization time of Ci-Na can exceed 70 min because of adding HA–Na, which is nearly doubled. The growth of inlet SO2 concentration has little effect on the desulfurization efficiency. The SO2 adsorption efficiency decreases with the increase of inlet flow gas. The presence of O2 improves the SO2 removal efficiency and prolongs the desulfurization time. Therefore, HA–Na plays a key role during SO2 absorption and can dramatically enhance the SO2 adsorption performance of Ci-Na solution.