Adsorption and mechanistic study for humic acid removal by magnetic biochar derived from forestry wastes functionalized with Mg/Al-LDH

Nitrate-Nitrogen Adsorption Characteristics and Mechanisms of Various Garden Waste Biochars

Nitrate-nitrogen (NO3--N) removal and garden waste disposal are critical concerns in urban environmental protection. In this study, biochars were produced by pyrolyzing various garden waste materials, including grass clippings (GC), Rosa chinensis Jacq. branches (RC), Prunus persica branches (PP), Armeniaca vulgaris Lam. branches (AV), Morus alba Linn. sp. branches (MA), Platycladus orientalis (L.) Franco branches (PO), Pinus tabuliformis Carrière branches (PT), and Sophorajaponica Linn. branches (SL) at three different temperatures (300 °C, 500 °C, and 700 °C). These biochars, labeled as GC300, GC500, GC700, and so on., were then used to adsorb NO3--N under various conditions, such as initial pH value, contact time, initial NO3--N concentration, and biochar dosage. Kinetic data were analyzed by pseudo-first-order and pseudo-second-order kinetic models. The equilibrium adsorption data were evaluated by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models. The results revealed that the biochar yields varied between 14.43% (PT700) and 47.09% (AV300) and were significantly influenced by the type of garden waste and decreased with increasing pyrolysis temperature, while the pH and ash content showed an opposite trend (p < 0.05). The efficiency of NO3--N removal was significantly influenced by the type of feedstock, preparation process, and adsorption conditions. Higher pH values had a negative influence on NO3--N adsorption, while longer contact time, higher initial concentration of NO3--N, and increased biochar dosage positively affected NO3--N adsorption. Most of the kinetic data were better fitted to the pseudo-second-order kinetic model (0.998 > R2 > 0.927). Positive b values obtained from the Temkin model indicated an exothermic process of NO3--N adsorption. The Langmuir model provided better fits for more equilibrium adsorption data than the Freundlich model, with the maximum NO3--N removal efficiency (62.11%) and adsorption capacity (1.339 mg·g-1) in PO700 under the conditions of pH = 2, biochar dosage = 50 mg·L-1, and a reaction time of 24 h. The outcomes of this study contribute valuable insights into garden waste disposal and NO3--N removal from wastewater, providing a theoretical basis for sustainable environmental management practices.

Removal of methylene blue by porous biochar obtained by KOH activation from bamboo biochar

A series of activated biochar (KBBC-700, KBBC-800 and KBBC-900) which were modified by KOH and pyrolysis at various temperatures from ball-milling bamboo powder were obtained. The physicochemical properties and pore structures of activated biochar were investigated by scanning electron microscopy (SEM), fourier transform infrared spectoscopy (FT-IR), X-ray diffraction (XRD) and N2 adsorption/desorption. The adsorption performance for the removal of methylene blue (MB) was deeply studied. The results showed that KBBC-900 obtained at activation temperature of 900 °C exhibited a great surface area which reached 562 m2/g with 0.460 cm3/g of total pore volume. The enhancement of adsorption capacity could be ascribed to the increase of surface oxygen-containing functional groups, aromatization and mesoporous channels. The adsorption capacity was up to 67.46 mg/g under the optimum adsorption parameters with 2 g/L of adsorbent dose, 11 of initial solution pH and 298 K of the reactive temperature. The adsorption capacity was 70.63% of the first time after the material was recycled for three cycles. The kinetics indicated that the adsorption equilibrium time for MB on KBBC-900 was of about 20 min with the data fitted better to the pseudo-second-order kinetics model. The adsorption process was mainly dominated by chemical adsorption. Meanwhile, the adsorption isotherm showed that the Langmuir model fitted the best, and thermodynamic parameters revealed that the adsorption reaction was the endothermic nature and the spontaneous process. Adsorption of MB mainly attributed to electrostatic interactions, cation-π electron interaction and redox reaction. This study suggested that the activated biochar obtained by KOH activation from bamboo biochar has great potentials in the practical application to remove MB from wastewater.

Adsorption kinetics and mechanism of atrazine on iron-modified algal residue biochar in the presence of soil

Atrazine has been widely used as an herbicide, and its harm has attracted more and more attention. In this study, magnetic algal residue biochar (MARB) was prepared from algae residue, a by-product of aquaculture, by ball milling it with ferric oxide to study the adsorption and removal of the triazine herbicide atrazine in a soil medium. The adsorption kinetics and isotherm results showed that atrazine removal by MARB reached 95.5% within 8 h at a concentration of 10 mg·L^-1, but the removal rate dropped to 78.4% in the soil medium. The pseudo-first- and pseudo-second-order kinetics and Langmuir isotherms best described atrazine adsorption on MARB. It is estimated that the maximum adsorption capacity of MARB can reach 10.63 mg·g^-1. The effects of pH, humic acids, and cations on the adsorption performance of MARB for atrazine were also studied. When pH was 3, the adsorption capacity of MARB was twice that of other pHs. Only in the presence of 50 mg·L^-1 HA and 0.1 mol·L^-1 NH₄⁺, Na, and K, the adsorption capacity of MARB to AT decreased by 8% and 13%, respectively. The results showed that MARB had a stable removal profile over a wide range of conditions. The adsorption mechanisms involved multiple interaction forms, among which the introduction of iron oxide promoted hydrogen bonding formation and π-π interactions by enriching -OH and -COO on the surface of MARB. Overall, the magnetic biochar prepared in this study can be used as an effective adsorbent to remove atrazine in complex environments and is ideal for algal biomass waste treatment and environmental governance.^+.

Study on the role of AlOOH in fluorescence correction and depth purification of Cyclops water

Protein-like substances produced by biochemical reactions after disinfection of Zooplankton like Cyclops and humic substances in natural water are the main components of NOM (Natural organic matter). To eliminate early warning interference in the fluorescence detection of organic matter in natural water, a clustered flower-like AlOOH (aluminum oxide hydroxide) sorbent was prepared. HA (humic acid) and amino acids were selected as mimics of humic substances and protein-like substances in natural water. The results demonstrate that the adsorbent can selectively adsorb HA from the simulated mixed solution and restore the fluorescence properties of tryptophan and tyrosine. Based on these results, a stepwise fluorescence detection strategy was developed and used in natural water rich in zooplanktonic Cyclops. The results show that the established stepwise fluorescence strategy can well overcome the interference caused by fluorescence quenching. The sorbent was also used for water quality control to enhance coagulation treatment. Finally, trial runs of the water plant demonstrated its effectiveness and suggested a potential control method for early warning and monitoring of water quality.

Type-wide biochars loaded with Mg/Al layered double hydroxide as adsorbent for phosphate and mixed heavy metal ions in water

This study discussed the adsorption of mixed heavy metal ions (Cu²⁺, Co²⁺, Pb²⁺) and phosphate ions by ten pristine biochars and those with precipitated Mg/Al layered double hydroxide (LDH). The pristine biochars have adsorption capacities of 6.9-13.4 mg/g for Cu²⁺, 1.1-9.7 mg/g for Co²⁺, 7.8-20.7 mg/g for Pb²⁺, and 0.8-4.9 mg/g for PO₄^3-. The LDH-biochars have markedly increased adsorption capacities of 20.4-25.8 mg/g for Cu²⁺, 8.6-15.0 mg/g for Co²⁺, 26.5-40.4 mg/g for Pb²⁺ with mixed metal ions, and 13.0-21.8 mg/g for PO₄^3-. Part of the Mg ions but Al ions are released from the LDH-biochars during adsorption, counting less than 7.2% of the adsorbed ions. The pristine biochars have specific adsorption sites for Cu²⁺ and Co²⁺, separate Pb²⁺ sites related to ether groups on biochar, and areal-dependent sites for PO₄^3-. There is no universal adsorption mechanism corresponding to mixed metal ion adsorption for individual pristine biochar involving different contributions of C-O-C, C-O-H, and CO groups and graphitic-N, pyrrolic-N, and pyridine-N groups. The LDH complexes with hydroxyl and carbonyl groups of biochar, and the LDH interacts with biochar's ether groups, which contributes to metal adsorption, against the conception that the biochar is merely a carrier of LDH as adsorbents.

Textural properties and adsorption behavior of Zn-Mg-Al layered double hydroxide upon crystal violet dye removal as a low cost, effective, and recyclable adsorbent

The preparation of adsorbents plays a vital role in the adsorption method. In particular, many adsorbents with high specific surface areas and unique shapes are essential for the adsorption strategy. A Zn-Mg-Al/layer double hydroxide (LDH) was designed in this study using a simple co-precipitation process. Adsorbent based on Zn-Mg-Al/LDH was used to remove crystal violet (CV) from the wastewater. The impacts of the initial dye concentration, pH, and temperature on CV adsorption performance were systematically examined. The adsorbents were analyzed both before and after adsorption using FTIR, XRD, and SEM. The roughness parameters and surface morphologies of the produced LDH were estimated using 3D SEM images. Under the best conditions (dose of adsorbent = 0.07 g and pH = 9), the maximum adsorption capacity has been achieved. Adsorption kinetics studies revealed that the reaction that led to the adsorption of CV dye onto Zn-Mg-Al/LDH was a pseudo-second-order model. Additionally, intraparticle diffusion suggests that Zn-Mg-Al/LDH has a fast diffusion constant for CV molecules (0.251 mg/(g min^1/2)). Furthermore, as predicted by the Langmuir model, the maximal Zn-Mg-Al/LDH adsorption capacity of CV was 64.80 mg/g. The CV dimensionless separation factor (R_L) onto Zn-Mg-Al/LDH was 0.769, indicating that adsorption was favorable. The effect of temperature was performed at 25, 35, and 45 °C in order to establish the thermodynamic parameters ∆H^o, ∆S^o, and ∆G^o. The computed values indicated exothermic and spontaneous adsorption processes. The study presented here might be used to develop new adsorbents with enhanced adsorption capabilities for the purpose of protecting the water environment.

Selective Adsorption of Direct Group Anionic Dyes on Layered Double Hydroxide-Chitosan Composites

In this research, the potential of M2+/Al intercalated chitosan has been evaluated and good ability to reduce dyes in an aqueous solution. M2+/Al intercalated chitosan was prepared by anion exchange method and coprecipitation in a nitrogen atmosphere. Selectivity adsorption was studied to maintain the ability of M2+/Al intercalated chitosan for particle size of direct dyes (direct green, direct red, and direct yellow). To evaluate the adsorption process, M2+/Al intercalated chitosan was conducted with kinetic, isotherm, and thermodynamic parameters. The kinetic data fitted well by pseudo-second order and isotherm fitted Langmuir isotherm with qmax obtained 294.11 and 322.58 mg/g for Zn/Al-chitosan and Mg/Al-chitosan, respectively. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Transport characteristics of polystyrene microplastics in saturated porous media with biochar/Fe3O4-biochar under various chemical conditions

Magnetically modified biochar, with a rougher surface and more positive surface charge, may interact with microplastics (MPs) after being applied to soil, potentially altering the fate and transport of MPs in porous media. In this study, the transport and retention behavior of polystyrene microplastics (PSMPs) in a sandy porous media mixed with biochar/Fe₃O₄ modified biochar (Fe₃O₄-biochar) was investigated under various chemical conditions (humic acid (HA), ionic strength (IS) and cationic types (Na⁺/Ca²⁺)). The results showed that the addition of biochar and Fe₃O₄-biochar can hinder the transport of PSMPs in porous media without HA, and that Fe₃O₄-biochar was more effective in inhibiting the transport of PSMPs through electrostatic adsorption and complexation, with an optimum retention efficiency of 92.36 %. HA significantly attenuated the retention of PSMPs in both porous media through electrostatic repulsion, steric resistance and competitive adsorption under 1 mM Na⁺ solutions, and the mobility of PSMPs in Fe₃O₄-biochar/sand was enhanced more significantly than in biochar/sand with the increase of HA concentration. IS significantly inhibited the transport of PSMPs in both porous media in the absence of HA, but there was an antagonistic effect of HA and IS on the transport of PSMPs in the presence of HA, with the facilitative effect of HA being stronger than the inhibitory effect of IS. Ca²⁺ was consistently more effective in inhibiting the transport of PSMPs than Na⁺ under all test conditions, and HA promoted the transport of PSMPs in all Na⁺ solutions, while it inhibited the transport of PSMPs in high IS (10 mM) with Ca²⁺ solutions. In addition, HA, Fe₃O₄-biochar and PSMPs tend to form larger aggregates under the complex interactions of Ca²⁺, leading to increased retention of PSMPs in porous media. The two-site kinetic retention models suggested that the retention of PSMPs in porous media with biochar was predominantly reversible attachment effect, while retention in porous media with Fe₃O₄-biochar was predominantly an irreversible straining effect.

A stable Fe/Co bimetallic modified biochar for ofloxacin removal from water: adsorption behavior and mechanisms

In this study, Fe-Co-modified biochar (FMBC) loaded with iron (Fe) and cobalt (Co) bimetals after NaOH activation was prepared by pyrolysis using forestry waste cedar bark as a raw material to study its properties and the adsorption of ofloxacin (OFX). The surface structure and chemical properties were analyzed by BET, SEM-EDS, XRD, XPS, and FTIR characterization, and the results showed that the FMBC possessed a larger specific surface area and abundant surface functional groups. FMBC conformed to pseudo-second-order kinetic and Langmuir isotherm models, indicating that the OFX adsorption process on FMBC was a monolayer adsorption process and controlled by chemisorption. The saturation adsorption capacity of FMBC was 10 times higher than that of cedar bark biochar (BC). In addition, the effects of initial pH and coexisting ions on the adsorption process were investigated, and FMBC showed good adsorption, with the best adsorption capacity at pH = 7. Multiple adsorption mechanisms, including physical and chemical interactions, were involved in the adsorption of OFX by FMBC. TG, metal leaching, different water sources, and VSM tests showed that FMBC had good stability and was easily separated from water. Finally, the reusability performance of FMBC was investigated by various methods, and after five cycles it could still reach 75.78-89.31% of the adsorption capacity before recycling. Therefore, the FMBC synthesized in this study is a promising new adsorbent.