Shape-selective adsorption mechanism of CS-Z1 microporous molecular sieve for organic pollutants

Highly Porous Multiwalled Carbon Nanotube-Foam Composite for Batch Adsorption Performances of Dyes

Treatment of dye pollutants prior to their release into the environment remains a formidable challenge, persisting as a longstanding issue. This study focuses on the development of a multiwalled carbon nanotube-foam (MWCNT-foam) composite through low-temperature chemical fusion (LTFC), resulting in a composite with a remarkably high accessible surface area (>475 m2 g-1). The MWCNT-foam composite exhibits a three-dimensional porous structure and demonstrates a notable affinity for organic dye adsorption. The efficacy of this composite was evaluated against various cationic dyes such as Methylene blue (MB) and Crystal Violet (CV) as well as anionic dyes such as Congo red (CR) and Eriochrome black T (EB), and the composite showed removal rates exceeding 99%. Furthermore, the study delved into the impact of the initial dye concentration, adsorbent dosage, kinetics, and other factors on the performance of the MWCNT-foam composite. The adsorption process achieved equilibrium in 10 min and strongly correlated with the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity of MWCNT-foam for MB, CV, CR, and EB was found to be 168.63, 147.49, 99.50, and 93.11 mg g-1, respectively. In order to showcase the potential of this material for continuous adsorption, a specialized cartridge was designed and employed to treat dye solutions, demonstrating the feasibility of continuous mode adsorption.

Basic magnesium sulfate@TiO2 composite for efficient adsorption and photocatalytic degradation of 4-dodecylmorpholine in brine

More than 70% of the potash fertilizer globally is produced by the froth flotation process, in which 4-dodecylmorpholine (DMP) serves as a reverse flotation agent. As the potash fertilizer production rapidly rises, the increased DMP levels in discharged brine pose a threat to the production of high-value chemicals. In this paper, composite particles of basic magnesium sulfate@TiO2 (BMS@TiO2) were prepared using a simple and mild loading method. These particles were utilized for the adsorption and photocatalytic degradation of DMP in brine. Compared with normal powdered materials, the granular BMS@TiO2 in this study can be easily separated from liquid, and the degradation intermediates will not enter the brine without causing secondary pollution. BMS@TiO2 consists of 5·1·7 phase (5Mg(OH)2·MgSO4·7H2O) whisker clusters embedding 2.3% TiO2. The adsorption equilibrium of DMP on BMS@TiO2 particles was achieved through hydrogen bonding and pore interception with the adsorption capacity of approximately 5 mg g-1 after 6 h. The photodegradation efficiency of DMP adsorbed on BMS@TiO2 reached about 92% within 16 h, which is compared with that of pure TiO2 nanoparticles. Additionally, excellent stability and recyclability of BMS@TiO2 were also observed in five cycle tests of adsorption and photocatalytic degradation of DMP, and the possible photocatalytic degradation pathways and mechanism of DMP are proposed following molecular electrostatic potential analysis. This work provides a sustainable and environmentally friendly approach for eliminating organic micropollutants from water environments.

Structural Regulation of Photocatalyst to Optimize Hydroxyl Radical Production Pathways for Highly Efficient Photocatalytic Oxidation

Ring-opening of phenol in wastewater is the pivotal step in photocatalytic degradation. The highly selective generation of catalytical active species (•OH) to facilitate this process presents a significant scientific challenge. Therefore, a novel approach for designing photocatalysts with single-atom containment in metal-covalent organic frameworks (M-COFs) is proposed. The selection of imine-linked COFs containing abundant N and O-chelate sites provides a solid foundation for anchoring metal atom. These dispersed metal atom possess rapid accumulation and transfer capabilities for photogenerated electrons, while the periodic π-conjugated structure in 2D-COFs establishes an effective platform. Additionally, the Lewis acid properties of imine bonds in COFs can enhance the adsorption capacity toward gases with Lewis base properties, such as O2 and N2 . It is demonstrated that the Pd2+ @Tp-TAPT, designed based on this concept, exhibits efficient oxygen adsorption and follows the reaction pathway of O2 →•O2 - →H2 O2 →•OH with high selectivity, thereby achieving completely degradation of refractory phenol through photocatalysis within 10 min. It is anticipated that the selective generation of catalytic active species via advanced material design concepts will serve as a significant reference for achieving precise material catalysis in the future.

Macroporous Aerogels Using High Internal Phase Pickering Emulsions for Adsorption of Dyes

The treatment of industrial printing and dyeing wastewater is the focus of the chemical environmental protection industry. Noticeably, the physical adsorption has attracted wide attention due to the selective dye adsorption, simple process, and convenient operation. New aerogels featuring low density and high porosity are regarded as ideal physical adsorption materials for sewage treatment. In this work, high internal phase Pickering emulsions were designed and prepared. The polysaccharide complex originating from sodium octenylsuccinate starch and chitosan serves as the stabilizer, water and hexane act as the external and internal phase, respectively. Acrylic acid was introduced into the external phase to initiate UV polymerization. The high internal phase Pickering emulsions as templates were removed through freeze-drying to produce aerogel materials with macroporous structures, the size of the pores: 43.54 ± 12.75 μm. The scanning electron microscopy (SEM) images show that the pore size of aerogel materials was similar to that of emulsion droplets, verifying the template role of emulsion in the polymerization process. In addition, aerogels possess good mechanical properties and can withstand a pressure of megapascal, exhibiting favorable stability when floating in water for a long time (6 months). Methyl violet, malachite green, methylene blue, and acridine orange in aqueous solution were selected as model dyes to explore the removal process and the mechanism. The adsorption was conformed to be the pseudo-second-order kinetic model and the Freundlich adsorption isotherm, namely, the dye adsorption of the aerogels was the multilayer adsorption on the uneven surface, and the mechanism of the adsorption was related to the π-π interaction.

Efficient adsorption of dyes from aqueous solution using a novel functionalized magnetic biochar: Synthesis, kinetics, isotherms, adsorption mechanism, and reusability

In this study, a novel adsorbent, dodecylbenzene sulfonic acid (DBSA) functionalized magnetic biochar (DBSA-Fe₃O₄@BC), was synthesized and used to efficiently remove dyes from aqueous solution. The results indicated that DBSA-Fe₃O₄@BC exhibited an excellent adsorption capacity for Rhodamine B (RhB), and the maximum adsorption capacity for RhB at 298 K was 367.67 mg/g, which was approximately 2.3-1.2 folds than that of BC, dodecylsulfonic acid functionalized biochar (DSA@BC), DBSA@BC, Fe₃O₄@BC, and DSA-Fe₃O₄@BC. The possible adsorption mechanisms for RhB adsorption by DBSA-Fe₃O₄@BC included pore filling, electrostatic attraction, H bond, and surface complexation. Importantly, structural control presented that the simultaneous introduction of alkyl and phenyl groups significantly enhanced RhB adsorption by DBSA-Fe₃O₄@BC through hydrophobic and π-π interaction. Combined ethanol (EtOH) desorption and H₂O₂ oxidation regeneration, DBSA-Fe₃O₄@BC remained high-performance for RhB adsorption after six cycles (97.44%), indicating its outstanding reusability. In summary, DBSA-Fe₃O₄@BC exhibited a prospective application for dyeing wastewater treatment.

Correction to the thermodynamic calculation using the Langmuir isotherm model by Saeed et al. (2022)

The thermodynamic parameters are usually used to analyze the spontaneity, thermal and random change of the adsorption process, therefore, it is important to obtain these parameters accurately. Recently, Saeed et al. (2022) published a high academic paper to reveal the adsorption properties and mechanism of dyes onto the chitosan composite of the iron metal-organic framework (CS/MOF-235). However, the thermodynamic parameters of ΔG and ΔS need to be corrected because their results affected the analyzed conclusions. In the present study, the thermodynamic parameters were recalculated by using the correct method through the Langmuir isotherm model. The recalculated thermodynamic parameters indicated that the change in free energy (ΔG) for the removal of methylene blue (MB) and methyl orange (MO) onto CS/MOF-235 is negative but not positive, meaning that the adsorption of dyes (MB and MO) is spontaneous but not non-spontaneous. The change in entropy (ΔS) is positive but not negative, implying that the randomness increases but not decreases during the adsorption process. The enthalpy (ΔH) maintained negative value and the entropy (ΔS) obtained positive value indicate that both of them are the driving forces of the adsorption.

Adsorption capacity of bio-char prepared from the pyrolysis of hazelnut shells at different temperatures

Biomass pyrolysis to produce bio-char is one of the scientific and effective means of utilizing biomass resources. Differ from previous studies, this paper explored the effect of pyrolysis temperature (400–1000 °C) on the adsorption capacity of hazelnut shell bio-char from two perspectives, including physical macroscopic structure and functional group microscopic adsorption, and the practical adsorption application tests on common 7 kinds of heavy metals in polluted water were further carried out. The results showed that the yield and adsorption of bio-char prepared at different pyrolysis temperatures varied significantly, as the temperature increased, bio-char yield and surface acid functional group content decreased, the adsorption rate on most of heavy metals increased firstly and then decreased (except for Cr6+), the adsorption capacity of bio-char prepared at above 600 °C was mainly affected by physical macroscopic structure, and at 800 °C, bio-char had a large number of pore structures, and pore structure has been fully developed, iodine adsorption value and BET specific surface area were 595.36 mg/g and 197.32 mg/m2, respectively, the adsorption effect of bio-char on Cr6+, Cd2+, Zn2+, Cu2+ and Ni2+ were best, and the adsorption rates were 45.23%, 44.14%, 60.11%, 61.28% and 65.07% respectively. It revealed that although the absorption effect of bio-chars prepared at different temperatures on different heavy metals had a great variation, large specific surface area and developed pore structure still played important role in the adsorption capacity of bio-char. These provided a reference for the application of hazelnut shell bio-char based on adsorption properties, especially absorbing heavy metals in polluted water.

Accurate Removal of Toxic Organic Pollutants from Complex Water Matrices

Characteristic emerging pollutants at low concentration have raised much attention for causing a bottleneck in water remediation, especially in complex water matrices where high concentration of interferents coexist. In the future, tailored treatment methods are therefore of increasing significance for accurate removal of target pollutants in different water matrices. This critical review focuses on the overall strategies for accurately removing highly toxic emerging pollutants in the presence of typical interferents. The main difficulties hindering the improvement of selectivity in complex matrices are analyzed, implying that it is difficult to adopt a universal approach for multiple targets and water substrates. Selective methods based on assorted principles are proposed aiming to improve the anti-interference ability. Thus, typical approaches and fundamentals to achieve selectivity are subsequently summarized including their mechanism, superiority and inferior position, application scope, improvement method and the bottlenecks. The results show that different methods may be applicable to certain conditions and target pollutants. To better understand the mechanism of each selective method and further select the appropriate method, advanced methods for qualitative and quantitative characterization of selectivity are presented. The processes of adsorption, interaction, electron transfer, and bond breaking are discussed. Some comparable selective quantitative methods are helpful for promoting the development of related fields. The research framework of selectivity removal and its fundamentals are established. Presently, although continuous advances and remarkable achievements have been attained in the selective removal of characteristic organic pollutants, there are still various substantial challenges and opportunities. It is hopeful to inspire the researches on the new generation of water and wastewater treatment technology, which can selectively and preferentially treat characteristic pollutants, and establish a reliable research framework to lead the direction of environmental science.

Adsorptive removal of aflatoxin B1 from vegetable oils via novel adsorbents derived from a metal-organic framework

Vegetable oils are essential daily diet, but they are simply contaminated with aflatoxin B₁ (AFB₁), a serious toxic compound to human health. Adsorption method due to the easy operation, high efficiency and low costing is set to become a main detoxification technique for AFB₁. Unfortunately, previous reported adsorbents were rarely used for detoxification in food industry since they cannot meet the criteria of large-scale production of edible oils. Metal-organic frameworks (MOFs) with unique textural properties could be favorable precursors for synthesis of advanced materials. In this research, three kinds of Cu-BTC MOF-derived porous materials were prepared by different carbonization temperature and characterized by XRD, SEM, FT-IR, and nitrogen adsorption-desorption techniques. Isotherm and kinetic studies on the adsorption behaviour of AFB₁ onto the three porous carbonaceous materials have been systematically conducted. The results revealed that the porous carbonaceous materials could act as the excellent adsorbents that were of enough adsorption sites for AFB₁, mainly due to the hierarchical porous structure and large surface areas for the enhancement of adsorption capacity. Notably, the porous carbonaceous materials could not only remove more than 90% of AFB₁ from real vegetable oils within 30 min, but also remain the treated oils at low cytotoxicity. Meanwhile, the detoxification process could little affect the quality of oils. Thus, the Cu-BTC MOF-derived porous carbonaceous materials with high efficiency, safe, practical and economic characteristics could be novel potential adsorbents used in the application of AFB₁ removal from contaminated vegetable oils.

Insight into the key factors in fast adsorption of organic pollutants by hierarchical porous biochar

Low-cost biochar adsorbent owning great potential for environmental remediation faces a bottleneck in application for its unsatisfied adsorption performance. Compared to the efforts on increasing adsorption capacity, improving adsorption speed which is important for treatment efficiency is often neglected. Herein, a hierarchical porous biochar (HPB) derived from shrimp shell was prepared and exhibited good adsorption capacity (Q_m>300 mg/g) and fast adsorptive equilibrium (≤10 min) towards three typical aromatic organics, whose adsorption universality was further proved by two-way ANOVA analysis. Whereafter, model analysis demonstrated that, the adsorptive forms (mono- and multi-layers) on HPB depended on whether the contaminant is charged. Compared to the benzene-ring site of organics, the charged site contributed 5.13 times to adsorption promotion in monolayer but -0.49 times in inhibition for multilayers forms. Simultaneously, functional group sites contributed relatively weak (0.023 to 0.342 times only). Following structural control revealed that, hierarchical pore structure of HPB was the key for the fast adsorption speed, and highly graphitic structure was important for the high adsorption capacity. This study aims to provide an advanced biochar adsorbent, not only in adsorption capacity but also in adsorptive speed, and reveal the relationship between the structure and adsorption performance of biochar.

Graphene oxide aerogel assembled by dimethylaminopropylamine /N-isopropylethylenediamine for the removal of copper ions

Graphene Oxide Monolith composites (GOMs) were prepared using dimethylaminopropylamine (DMPDA) and N-isopropylethylenediamine (IPEDA) with one-step method in water medium, respectively. Fourier transform-infrared (FTIR), X-Ray Diffraction (XRD) tests proved the formation of new structure and credible interactions between crosslinkers and GO. Scanning electron microscopy (SEM) showed distinct change of morphology after complexing. Bath adsorption tests suggested that the fast adsorption of copper ions (II) was strongly affected by pH, ionic strength, temperature, and concentration, etc.. Isothermal Langmuir and Freundlich kinetic model showed the different degree of fitting conformity according to different conditions. SEM and XRD further provided a supporter of adsorption of copper ions onto GOMs, and Density functional theory (DFT) was used to analyze the crosslinking details of DMPDA and GO and the adsorption mechanism of copper ions. The theoretical calculation results clarified an efficacious and quantitative understanding for the crosslinking and adsorption mechanism.