Selective removal of anionic and cationic dyes by magnetic Fe3O4-loaded amine-modified hydrochar

Facile synthesis of amino-modified magnetic covalent organic framework for the efficient extraction and determination of anionic azo dyes in carbonated beverages

In this work, a novel magnetic covalent organic framework (COF (TpPa-NH2) @ Fe3O4) was prepared via two step by simple solvent method for the extraction of anionic azo dye residues in food. The as-prepared COF (TpPa-NH2) @ Fe3O4 nanocomposite was characterised by scanning electron microscope, transmission electron microscope, Fourier transform-infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. Before high-performance liquid chromatography with ultraviolet detection (HPLC-UV) determination, it was used as magnetic adsorbent for magnetic solid-phase extraction (MSPE) to extract and pre-concentrate three anionic azo dyes in carbonated beverage samples. The several key extraction and desorption parameters affecting the extraction recovery rate were investigated, including extraction time, pH of the solution, amount of material, adsorption time, elution solvent, pH of elution solvent, type of elution solvent, elution volume and elution time. Under optimised conditions, this method has good linearity between 5 and 500 μg L-1 (correlation coefficient > 0.9986). The limit of detection was 2.3-3.4 μg L-1. The recoveries of the samples were between 87.5 and 96.9%, and the relative standard deviation lower than 4.6%. The developed method has broad application prospects for the analysis of anionic azo dyes in carbonated beverages.

A review: Hydrochar as potential adsorbents for wastewater treatment and CO2 adsorption

To valorize the biomass and organic waste, hydrothermal carbonization (HTC) stands out as a highly efficient and promising pathway given its intrinsic advantages over other thermochemical processes. Hydrochar, as the main product obtained from HTC, is widely applied as a fuel source and soil conditioner. Aside from these applications, hydrochar can be either directly used or modified as bio-adsorbents for environmental remediation. This potential arises from its tunable surface chemistry and its suitability to act as a precursor for activated or engineered carbon. In view of the importance of this topic, this review offers a thorough examination of the research progress for using hydrochar and its modified forms to remove organic dyes (cationic and anionic dyes), heavy metals, herbicides/pesticides, pharmaceuticals, and CO2. The review also sheds light on the fundamental chemistry involved in HTC of biomass and the major analytical techniques applied for understanding surface chemistry of hydrochar and modified hydrochar. The knowledge gaps and potential hurdles are identified to highlight the challenges and prospects of this research field with a summary of the key findings from this review. Overall, this article provides valuable insights and directives and pinpoints the areas meriting further investigation in the application potential of hydrochar in wastewater management and CO2 capture.

Incorporation of Cellulose-Based Aerogels into Textile Structures

Given their exceptional attributes, aerogels are viewed as a material with immense potential. Being a natural polymer, cellulose offers the advantage of being both replenishable and capable of breaking down naturally. Cellulose-derived aerogels encompass the replenish ability, biocompatible nature, and ability to degrade naturally inherent in cellulose, along with additional benefits like minimal weight, extensive porosity, and expansive specific surface area. Even with increasing appreciation and acceptance, the undiscovered possibilities of aerogels within the textiles sphere continue to be predominantly uninvestigated. In this context, we outline the latest advancements in the study of cellulose aerogels' formulation and their diverse impacts on textile formations. Drawing from the latest studies, we reviewed the materials used for the creation of various kinds of cellulose-focused aerogels and their properties, analytical techniques, and multiple functionalities in relation to textiles. This comprehensive analysis extensively covers the diverse strategies employed to enhance the multifunctionality of cellulose-based aerogels in the textiles industry. Additionally, we focused on the global market size of bio-derivative aerogels, companies in the industry producing goods, and prospects moving forward.

Porous polymer magnetic adsorbents for dye wastewater treatment

Dye wastewater discharged from industries has caused serious environmental problems. The recent decade has witnessed adsorption technology emerging as an advanced dye wastewater treatment method with great potential Therefore, we fabricated two kinds of magnetic porous adsorbents (HSF and HSVF) with different specific surface areas and activity sites. Both of which exhibit excellent performance with remarkable dye adsorption capacities, especially HSVF. We further investigated their adsorption kinetic and isotherm in detail. Therein, HSVF showed a nice desorption capacity, and it could be recycled rapidly by magnetism, which exhibited the advantages of effective, easy operation, and low cost. In addition, their adsorption kinetic and isotherm were further studied and compared in detail. The results revealed that introducing strong active sites could improve both the adsorption capacity and rate effectively even though sacrificing part of specific surface areas, indicating that active sites might play a dominant role during the dye adsorption process.

Simultaneously Cationic and Anionic Dyes Elimination via Magnetic Hydrochar Prepared from Copper Slag and Pinewood Sawdust

In practical wastewater, cationic and anionic dyes usually coexist, while synergistic removal of these pollutants is difficult due to their relatively opposite properties. In this work, copper slag (CS) modified hydrochar (CSHC) was designed as functional material by the one-pot method. Based on characterizations, the Fe species in CS can be converted to zero-valent iron and loaded onto a hydrochar substrate. The CSHC exhibited efficient removal rates for both cationic dyes (methylene blue, MB) and anionic dyes (methyl orange, MO), with a maximum capacity of 278.21 and 357.02 mg·g^-1, respectively, which was significantly higher than that of unmodified ones. The surface interactions of MB and MO between CSHC were mimicked by the Langmuir model and the pseudo-second-order model. In addition, the magnetic properties of CSHC were also observed, and the good magnetic properties enabled the adsorbent to be quickly separated from the solution with the help of magnets. The adsorption mechanisms include pore filling, complexation, precipitation, and electrostatic attraction. Moreover, the recycling experiments demonstrated the potential regenerative performance of CSHC. All these results shed light on the co-removal of cationic and anionic contaminates via these industrial by-products derived from environmental remediation materials.

Synergistic effect in simultaneous removal of cationic and anionic heavy metals by nitrogen heteroatom doped hydrochar from aqueous solutions

Industrial wastewater typically contains both cationic and anionic heavy metals; therefore, their simultaneous removal must be considered to ensure environmental sustainability. Herein, nitrogen heteroatom (N) doped hydrochar derived from corncob was prepared via facile NH₄Cl-aided hydrothermal carbonization and used for the simultaneous adsorption of divalent copper (Cu(II)) and hexavalent chromium (Cr(VI)) in aqueous solutions. During hydrothermal carbonization, NH₄Cl played a vital role as the porogen and N dopant, which contributed to the efficient adsorption affinity toward coexisting Cu(II) and Cr(VI). The theoretical maximum adsorption capacities of the N-doped hydrochar were determined to be 1.223 mmol/g for Cu(II) and 1.995 mmol/g for Cr(VI), which were much better than those of the pristine hydrochar. Furthermore, in the binary-component system, the synergistic effect between Cu(II) and Cr(VI) significantly promoted the adsorption affinity of N-doped hydrochar, resulting in adsorption capacities for Cu(II) and Cr(VI) 9.48 and 1.92 times higher than those of the single-component system, respectively. A series of adsorption experiments and spectroscopic analyses demonstrated that multiple mechanisms, including electrostatic shielding, cation bridging, and redox reactions, mutually contributed to the synergistic effect in the adsorption of coexisting Cu(II) and Cr(VI). Overall, the N-doped hydrochar proved to be effective in simultaneously removing both cationic and anionic heavy metal pollutants.

Multiple roles of ferric chloride in preparing efficient magnetic hydrochar for sorption of methylene blue from water solutions

Highly efficient and cheap magnetic materials have application prospects in wastewater treatment. Herein, Fe₃O₄-loaded hydrochar (HC-Fe₃O₄) was obtained from hydrothermal carbonization (HTC) of bamboo with FeCl₃ and then added with FeCl₃ to form a magnetic sorbent via simple precipitation. The HC-Fe₃O₄ was characterized with various instruments. The characterizations show FeCl₃ plays at least two roles as a catalyst and an oxidant in HTC. The specific surface area of hydrochar enlarged from 39.9731 to 60.9887 m²·g^-1 after the addition of FeCl₃ during HTC, which showed FeCl₃ acted as a catalyst in HTC. XRD indicated Fe₃O₄ was formed by the structure of HC-Fe₃O₄, which indicated Fe(III) was reduced to Fe(II) during HTC. Sorption of methylene blue (MB) onto HC-Fe₃O₄ was better fitted by the Langmuir isotherm and pseudo-second-order kinetic models. Sorption is a spontaneous thermodynamic endothermic process and HC-Fe₃O₄ is easily separated by an applied magnetic field and reused.

Co-Carbonized Waste Polythene/Sugarcane Bagasse Nanocomposite for Aqueous Environmental Remediation Applications

The conversion of worthless municipal solid wastes to valuables is a major step towards environmental conservation and sustainability. This work successfully proposed a technique to utilize the two most commonly available municipal solid wastes viz polythene (PE) and sugarcane bagasse (SB) for water decolorization application. An SBPE composite material was developed and co-pyrolyzed under an inert atmosphere to develop the activated SBPEAC composite. Both SBPE and SBPEAC composites were characterized to analyze their morphological characteristics, specific surface area, chemical functional groups, and elemental composition. The adsorption efficacies of the composites were comparatively tested in the removal of malachite green (MG) from water. The SBPEAC composite had a specific surface area of 284.5 m²/g and a pore size of ~1.33 nm. Batch-scale experiments revealed that the SBPEAC composite performed better toward MG adsorption compared to the SBPE composite. The maximum MG uptakes at 318 K on SBPEAC and SBPE were 926.6 and 375.6 mg/g, respectively. The adsorption of MG on both composites was endothermic. The isotherm and kinetic modeling data for MG adsorption on SBPEAC was fitted to pseudo-second-order kinetic and Langmuir isotherm models, while Elovich kinetic and D-R isotherm models were better fitted for MG adsorption on SBPE. Mechanistically, the MG adsorption on both SBPE and SBPEAC composites involved electrostatic interaction, H-bonding, and π-π/n-π interactions.

A review on hydrothermal carbonization of potential biomass wastes, characterization and environmental applications of hydrochar, and biorefinery perspectives of the process

It is imperative to search for appropriate processes to convert wastes into energy, chemicals, and materials to establish a circular bio-economy toward sustainable development. Concerning waste biomass valorization, hydrothermal carbonization (HTC) is a promising route given its advantages over other thermochemical processes. From that perspective, this article reviewed the HTC of potential biomass wastes, the characterization and environmental utilization of hydrochar, and the biorefinery potential of this process. Crop and forestry residues and sewage sludge are two categories of biomass wastes (lignocellulosic and non-lignocellulosic, respectively) readily available for HTC or even co-hydrothermal carbonization (Co-HTC). The temperature, reaction time, and solid-to-liquid ratio utilized in HTC/Co-HTC of those biomass wastes were reported to range from 140 to 370 °C, 0.05 to 48 h, and 1/47 to 1/1, respectively, providing hydrochar yields of up to 94 % according to the process conditions. Hydrochar characterization by different techniques to determine its physicochemical properties is crucial to defining the best applications for this material. In the environmental field, hydrochar might be suitable for removing pollutants from aqueous systems, ameliorating soils, adsorbing atmospheric pollutants, working as an energy carrier, and performing carbon sequestration. But this material could also be employed in other areas (e.g., catalysis). Regarding the effluent from HTC/Co-HTC, this byproduct has the potential for serving as feedstock in other processes, such as anaerobic digestion and microalgae cultivation. These opportunities have aroused the industry interest in HTC since 2010, and the number of industrial-scale HTC plants and patent document applications has increased. The hydrochar patents are concentrated in China (77.6 %), the United States (10.6 %), the Republic of Korea (3.5 %), and Germany (3.5 %). Therefore, considering the possibilities of converting their product (hydrochar) and byproduct (effluent) into energy, chemicals, and materials, HTC or Co-HTC could work as the first step of a biorefinery. And this approach would completely agree with circular bioeconomy principles.

Enhanced removal of Eriochrome Black T from water using biochar/layered double hydroxide/chitosan hybrid composite: Performance evaluation and optimization using BBD-RSM approach

In this research work, a novel hybrid composite consisting of biochar (B), layered double hydroxide (CuFe) and chitosan (CS) (B-CuFe-CS) was produced using an ultrasonication-assisted co-precipitation method. The resultant composite was employed for adsorptive removal of Eriochrome black T (EBT) from water. Physicochemical characterization indicated that the B-CuFe-CS containing 10 wt % CS exhibited a heterogeneous structure with better crystallographic and textural characteristics. The B-CuFe-CS with abundant surface functionalities (-CO, -C-O, -OH, -NO_3, and MMO), facilitates faster and enhanced removal of the EBT. The kinetic results showed better fitting to the pseudo-second order model, and equilibrium was achieved within 30 min. Equilibrium data was well explained by Langmuir and Redlich Peterson isotherm models (R² > 0.98), indicating the EBT removal onto B-CuFe-CS followed monolayer adsorption. The maximum adsorption capacity was 806.4 mg/g, which was higher than pristine B-CuFe (476.19 mg/g) and many other adsorbents. The spectroscopic analysis (FTIR and XPS) and experimental results suggested that EBT adsorption is mainly governed by electrostatic, chemical and anion-exchange interactions. It is evident from these results that coupling B-CuFe composite with bio-filler (chitosan) resulted in an efficient bio-adsorbent to effectively purify dye-contaminated water streams.

Preparation and application of polyethyleneimine-modified corncob magnetic gel for removal of Pb(ii) and Cu(ii) ions from aqueous solution

As a biomass resource, corncob is a kind of agricultural by-product with wide sources and low cost. Because its composition contains a large number of functional polymers such as cellulose, chitosan, and semi chitosan, corncob can be chemically modified to prepare a variety of adsorption materials. In this study, a magnetic gel material (PEI-CC@Fe3O4) consisting of corncob modified by glutaraldehyde-crosslinked polyethyleneimine (PEI) was successfully prepared and applied to the adsorption of heavy metal ions in aqueous solutions. The structure, thermal stability, and adsorption of heavy metal ions of the magnetic gel material (PEI-CC@Fe3O4) were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction phase analysis (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results showed that PEI was crosslinked to the corncob through Aldol reaction and Schiff-base reaction. The heavy metal ion adsorption experiment showed that the PEI-CC@Fe3O4 had better adsorption toward divalent copper ions and divalent lead ions at 303 K, and the maximum adsorption capacities reached 459.4 mg g-1 and 290.8 mg g-1, respectively. Moreover, the study of isothermal adsorption and adsorption kinetics shows that the adsorption process is pseudo-second-order kinetics model adsorption, which belongs to Langmuir isothermal adsorption. Such excellent adsorption performance will contribute to the application of corncob biomass materials in industrial polluted wastewater.

Efficient adsorption of methylene blue on carboxylate-rich hydrochar prepared by one-step hydrothermal carbonization of bamboo and acrylic acid with ammonium persulphate

Hydrochar (AAHC) with rich carboxylate groups was prepared by one-step hydrothermal carbonization (HTC) of bamboo and acrylic acid with the presence of ammonium persulphate, and then activated by a sodium hydroxide solution. AAHC was featured by elemental analysis, SEM, XPS, FTIR, Zeta potential analysis and N₂ adsorption-desorption isotherms, and applied to test adsorptive ability of methylene blue (MB) by batch sorption experiments. Despite a small Brunauer-Emmett-Teller (BET) surface area of 5.03 m²·g^-1, AAHC has excellent MB adsorbing capacity owing to the richness of carboxylate groups. Compared with hydrochar produced without adding ammonium persulphate, AAHC exhibits larger BET surface, pore volume and carboxylate groups, indicating a small amount of ammonium persulfate plays an important role in HTC in addition to the free radical initiator. This work provides a facile and cheap method combining HTC and polymerization for preparation of carboxylate-rich hydrochar.

Characterization of Bio-Adsorbents Produced by Hydrothermal Carbonization of Corn Stover: Application on the Adsorption of Acetic Acid from Aqueous Solutions

In this work, the influence of temperature on textural, morphological, and crystalline characterization of bio-adsorbents produced by hydrothermal carbonization (HTC) of corn stover was systematically investigated. HTC was conducted at 175, 200, 225, and 250 °C, 240 min, heating rate of 2.0 °C/min, and biomass-to-H2O proportion of 1:10, using a reactor of 18.927 L. The textural, morphological, crystalline, and elemental characterization of hydro-chars was analyzed by TG/DTG/DTA, SEM, EDX, XRD, BET, and elemental analysis. With increasing process temperature, the carbon content increased and that of oxygen and hydrogen diminished, as indicated by elemental analysis (C, N, H, and S). TG/DTG analysis showed that higher temperatures favor the thermal stability of hydro-chars. The hydro-char obtained at 250 °C presented the highest thermal stability. SEM images of hydro-chars obtained at 175 and 200 °C indicated a rigid and well-organized fiber structure, demonstrating that temperature had almost no effect on the biomass structure. On the other hand, SEM images of hydro-chars obtained at 225 and 250 °C indicated that hydro-char structure consists of agglomerated micro-spheres and heterogeneous structures with nonuniform geometry (fragmentation), indicating that cellulose and hemi-cellulose were decomposed. EDX analysis showed that carbon content of hydro-chars increases and that of oxygen diminish, as process temperature increases. The diffractograms (XRD) identified the occurrence of peaks of higher intensity of graphite (C) as the temperature increased, as well as a decrease of peaks intensity for crystalline cellulose, demonstrating that higher temperatures favor the formation of crystalline-phase graphite (C). The BET analysis showed 4.35 m2/g surface area, pore volume of 0.0186 cm3/g, and average pore width of 17.08 μm. The solid phase product (bio-adsorbent) obtained by hydrothermal processing of corn stover at 250 °C, 240 min, and biomass/H2O proportion of 1:10, was activated chemically with 2.0 M NaOH and 2.0 M HCl solutions to investigate the adsorption of CH3COOH. The influence of initial acetic acid concentrations (1.0, 2.0, 3.0, and 4.0 mg/mL) was investigated. The kinetics of adsorption were investigated at different times (30, 60, 120, 240, 480, and 960 s). The adsorption isotherms showed that chemically activated hydro-chars were able to recover acetic acid from aqueous solutions. In addition, activation of hydro-char with NaOH was more effective than that with HCl.

Enhanced removal of Cr(VI) by nitrogen-doped hydrochar prepared from bamboo and ammonium chloride

N-doped biochar can effectively eliminate toxic Cr(VI). Here, N-doped hydrochar (NHC) was successfully synthesized by one-pot hydrothermal carbonization (HTC) of NH₄Cl and bamboo, and employed to adsorb Cr(VI). The specific surface area, pore volume, and carbon and nitrogen contents of NHC all increase compared with the undoped hydrochar (HC). NH₄Cl acts as a cheap nitrogen source to enhance the nitrogen content of hydrochar and as an acid catalyst to accelerate hydrochar carbonization. Adsorption experiments show NHC has higher adsorption capacity than HC for Cr(VI). XPS and FTIR imply the dominant mechanisms of adsorbing Cr(VI) onto two hydrochars are electrostatic attraction, reduction and complexation, but the contributions of surface functional groups in two hydrochars for elimination of Cr(VI) differ. The doped nitrogen in NHC is pivotal in adsorbing and reducing Cr(VI). Hence, NHC prepared from bamboo and NH₄Cl by one-step HTC is a cheap and efficient adsorbent to eliminate aqueous Cr(VI).

Preparation of hydrochar with high adsorption performance for methylene blue by co-hydrothermal carbonization of polyvinyl chloride and bamboo

Polyvinyl chloride (PVC) was blended into bamboo powder during co-hydrothermal carbonization (Co-HTC) to understand the effects on the physicochemical properties and adsorbing ability of hydrochar. The properties of hydrochar were characterized by Zeta potential, elemental analyses, BET, FTIR, XPS, Boehm titration and SEM. The addition of PVC into bamboo in Co-HTC decreased the BET area, and pore volume and radius of hydrochar, but increased the contents of surface hydroxyl and carboxyl groups. The adsorption ability of hydrochar produced by addition of PVC at 473 K over methylene blue (MB) increased significantly. The main adsorption mechanism was electrostatic attraction by -N(CH₃)₂⁺ of MB and carboxylate of hydrochar, and hydrogen-bonding interaction through N atom of phenothiazine in MB and C-OH of hydrochar. Thus, Co-HTC offers a facile, green and economical alternative for conversion of waste into high-value adsorbents.

High effective adsorption of Pb(II) from solution by biochar derived from torrefaction of ammonium persulphate pretreated bamboo

Biochar was prepared by torrefaction of ammonium persulphate pretreated bamboo (labeled as APBC) and applied into elimination of Pb(II) from water solutions. APBC was characterized by N₂ adsorption-desorption isotherms, elemental and Zeta potential analyses, SEM-EDS, XPS, and FTIR. Abundant N- and O-containing groups appeared atop APBC. Batch sorption assays revealed that APBC had high affinity and strong sorption ability towards Pb(II). The high Pb(II) adsorbing ability was attributed to the high contents of N- and O-containing functional groups of APBC. The adsorption mechanism mainly occurred by inner-sphere surface complexation. Hence, torrefaction of ammonium persulphate pretreated bamboo is a promising strategy for producing efficient biochar that is applicable for industrial wastewater treatment.

Porous Organic Polymer Synthesized by Green Diazo-Coupling Reaction for Adsorptive Removal of Methylene Blue

A porous organic polymer (marked as DT-POP), which contains abundant free phenolic hydroxyl groups, is synthesized by the well-known green azo-coupling reaction in water, characterized, and utilized as an effective adsorbent for the elimination of methylene blue (MB) from water solutions. The presence of permanent mesopores, abundant active functional groups, and π-electron enrichment ascribed to phenyl rings make DT-POP an efficient adsorbent for MB due to strong hydrogen bonding, π-π, and electrostatic interactions with the cationic dye MB. DT-POP with high stability and high adsorption capacity can be reused many times and thus shows high applicability in pollutant disposal.