Effect of bifunctional acid on the porosity improvement of biomass-derived activated carbon for methylene blue adsorption

Revolutionizing wastewater treatment: A review on the role of advanced functional bio-based hydrogels

Water contamination poses a significant challenge to environmental and public health, necessitating sustainable wastewater treatment solutions. Adsorption is one of the most widely used techniques for purifying water, as it effectively removes contaminants by transferring them from the liquid phase to a solid surface. Bio-based hydrogel adsorbents are gaining popularity in wastewater treatment due to their versatility in fabrication and modification methods, which include blending, grafting, and crosslinking. Owning to their unique structure and large surface area, modified hydrogels containing reactive groups like amino, hydroxyl, and carboxyl, or functionalized hydrogels with inorganic nanoparticles particularly graphene nanomaterials, have demonstrated promising adsorption capabilities for both inorganic and organic contaminants. Bio-based hydrogels have excellent physicochemical properties and are non-toxic, environmentally friendly, and biodegradable, making them extremely effective at removing contaminants like heavy metal ions, dyes, pharmaceutical pollutants, and organic micropollutants. The versatility of hydrogels allows for various forms to be used, such as films, beads, and nanocomposites, providing flexibility in handling different contaminants like dyes, radionuclides, and heavy metals. Additionally, researchers also have shown the potential for recycling and regenerating post-treatment hydrogels. This approach not only addresses the challenges of wastewater treatment but also offers sustainable and effective solutions for mitigating water pollution.

Synthesis of Poly(GG-co-AAm-co-MAA), a Terpolymer Hydrogel for the Removal of Methyl Violet and Fuchsin Basic Dyes from Aqueous Solution

A novel adsorbent designated as terpolymer hydrogel (gellan gum-co-acrylamide-co-methacrylic acid) was prepared by free radical polymerization of gellan gum (GG), methacrylic acid (MAA), and acrylamide (AAm) using N,N-methylene bis-acrylamide (MBA) as cross-linker and ammonium per sulfate (APS) as the initiator of the reaction. The synthesized gel was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and thermogravimetric analysis (TGA) and was used for the adsorptive removal of methyl violet (MV) and Fuchsin Basic (FB) dyes from aqueous solution. The effect of temperature, contact time, pH, and concentration on them under the study adsorption process was evaluated. Freundlich isotherm and pseudo-second-order kinetic models were found to be best in fitting the isothermal and kinetics data. The water diffusion and % swelling of hydrogel were studied at various pH in distilled water and at neutral pH in tap water. The diffusion was found to be of Fickian type with a maximum swelling of 5132%. The maximum adsorption capacity was 233 mg/g against MV and 200 mg/g against FB dyes. The swelling and adsorption were pH dependent and increased with increase in pH. The enthalpy, Gibbs free energy, and entropy changes of adsorption for both the dyes indicated the adsorption process to be exothermic, feasible, and spontaneous. The hydrogel was successfully regenerated using acetone and distilled water for five cycles and still, its dye removal efficiency was 80% of its original value. The poly(GG-co-AAm-co-MAA) hydrogel successfully removed the selected dyes from water and could thus be used as an efficient alternative sorbent for cationic dye removal from aqueous solutions.

Efficient removal of heavy metal and antibiotics from wastewater by phosphate-modified hydrochar

The preparation, characterization and adsorption performance of the phosphate-modified hydrochar (P-hydrochar) for Pb(II) and ciprofloxacin removal are investigated. Pb(II) and ciprofloxacin adsorption behavior fit well with the Hill model with the adsorption capacity of 119.61 and 98.38 mg/g, respectively. Pb(II) and ciprofloxacin adsorption kinetic process are accurately described by the Pseudo-second-order. Pb(II) and ciprofloxacin have synergy in the binary contaminant system, which reveals that Pb(II) adsorption amount is augmented. While ciprofloxacin adsorption amount is also augmented at low Pb(II) concentration and hindered at high Pb(II) concentration. Pb(II) adsorption mechanisms on P-hydrochar (e.g. precipitation, π-π interaction and complexation) are different from the ciprofloxacin (e.g. hydrogen bonding, pore filling, electrostatic attraction). Pb(II) and ciprofloxacin adsorption process are further analyzed by the density functional theory. The coexisted ions have little influenced on Pb(II) and ciprofloxacin adsorption. P-hydrochar still has large Pb(II) and ciprofloxacin adsorption capacity after five cycles. This result indicates that poplar sawdust waste can be converted into an efficient adsorbent to remove Pb(II) and ciprofloxacin from wastewater,.

Nano-silica from white silica sand functionalized with PANI-SDS (SiO2/PANI-SDS) as an adsorbent for the elimination of methylene blue from aqueous media

Natural resources including sand are one of the best approaches for treating dye-polluted wastewater. The SiO2/PANI-SDS nanocomposite was synthesized by self-assembly and intermolecular interaction. The physicochemical features of the SiO2/PANI-SDS nanocomposite were explored by FT-IR, XRD, SEM, TEM, EDX, and N2 adsorption-desorption techniques to be evaluated as an adsorbent for the MB. The surface area of the SiO2/PANI-SDS is 23.317 m2/g, the pore size is 0.036 cm3/g, and the pore radius is 1.91 nm. Batch kinetic studies at different initial adsorbate, adsorbent and NaCl concentrations, and temperatures showed excellent pseudo-second-order. Several isotherm models were applied to evaluate the MB adsorption on the SiO2/PANI-SDS nanocomposite. According to R2 values the isotherm models were fitted in the following order: Langmuir > Dubinin-Radushkevich (D-R) > Freundlich. The adsorption/desorption process showed good reusability of the SiO2/PANI-SDS nanocomposite.

Adsorption of chloramphenicol from water using Carex meyeriana Kunth-derived hierarchical porous carbon with open channel arrays

A carbon material with both open macrochannel arrays and abundant micro/mesopores was prepared, characterized, and applied for removing chloramphenicol (CAP) from water. In the preparation process, Carex meyeriana Kunth (CM) with natural channel arrays was used as the precursor for producing the biochar, and NaOH was used for removing silicon and formatting micro- and mesopores of the porous carbon. The product (PCCM) exhibited the highest specific surface area (2700.24 m² g^-1) among the reported CM-derived porous carbons. The adsorption performances of PCCM were evaluated through batch adsorption experiments. The maximum adsorption capacity of PCCM toward CAP was 1659.43 mg g^-1. The adsorption mechanism was investigated with the aid of theoretical calculations. Moreover, PCCM exhibited better performance than other porous carbon adsorbents in fixed-bed experiments, which may be due to its structural advantages.

Efficient preparation of carbon nanospheres-anchored porous carbon materials and the investigation on pretreatment methods

Manufacturing high-performance activated carbon (AC) materials from abundant biomass at low temperature and short activation time is targeted by the green and sustainable chemical industry. Here, a 1980 m²/g of carbon nanospheres-anchored porous carbon material (PHAC) derived from waste sawdust was prepared by a method of H₃PO₄ hydrothermal combined with fast activation at 450 °C within 2.8 min. It is found that H₃PO₄ hydrothermal pretreatment could promote the dehydration of carbohydrates to form more unstable C = O structures, which were decomposed in the subsequent fast activation to form pore structures. In addition, this process is also conducive to the formation of carbon nanospheres, increasing the degree of graphitization and producing more graphite defects. The prepared PHAC showed good adsorption performance for different types of pollutants. This work provides a new insight for the preparation of high performance biomass based carbon materials under mild conditions.

Solar Light-Induced Methylene Blue Removal over TiO2/AC Composites and Photocatalytic Regeneration

TiO₂-containing photocatalysts, which combine TiO₂ with carbon-based materials, are promising materials for wastewater treatment due to synergistic photodegradation and adsorption phenomena. In this work, TiO₂/AC composites were produced by the in situ immobilization of TiO₂ nanoparticles over activated carbon (AC) derived from spent coffee grains, using different TiO₂/AC proportions. The TiO₂/AC composites were tested as adsorbents (dark) and as photocatalysts in a combined adsorption+photocatalytic process (solar irradiation) for methylene blue (MB) removal from ultrapure water, and from a secondary effluent (SecEf) of an urban wastewater treatment plant. All the materials were characterized by XRD (X-ray powder diffraction), N₂ adsorption–desorption isotherms at −196 °C, SEM (scanning electron microscopy), UV-Vis diffuse reflectance, FTIR (Fourier-transform infrared spectroscopy), TPD (temperature programmed desorption), XPS (X-ray photoelectron spectroscopy) and TGA (thermogravimetric analysis). The TiAC60 (60% C) composite presented the lowest band gap (1.84 eV), while, for TiAC29 (29% C), the value was close to that of bare TiO₂ (3.18 vs. 3.17 eV). Regardless of the material, the solar irradiation improved the percentage of MB discolouration when compared to adsorption in dark conditions. In the case of simultaneous adsorption+photocatalytic assays performed in ultrapure water, TiAC29 presented the fastest MB removal. Nevertheless, both TiAC29 and TiAC60 led to excellent MB removal percentages (96.1–98.1%). UV-induced photoregeneration was a promising strategy to recover the adsorption capacity of the materials, especially for TiAC60 and AC (>95%). When the assays were performed in SecEf, all the materials promoted discolouration percentages close to those obtained in ultrapure water. The bulk water parameters revealed that TiAC60 allowed the removal of a higher amount of MB, associated with the overall improvement of the SecEf quality.

O-N-S Self-Doped Hierarchical Porous Carbon Synthesized from Lotus Leaves with High Performance for Dye Adsorption

Three-dimensional porous carbon was fabricated using lotus leaves as a renewable precursor. The as-synthesized carbon had a high surface area (3601 m²/g), suitable O-N-S self-doping, and three-dimensional (3D) architecture with interconnected micro/meso/macropores, together with proper pore size distribution. Consequently, these admirable features endowed porous carbon as a superadsorbent for dye removal with ultrahigh adsorption capacity for rhodamine B (9444.39 mg/g) and reliable cyclability (>97% capacitance retention after 10 cycles). The adsorption of dye onto the as-prepared carbon was a spontaneous endothermic process and followed the pseudo-second-order kinetic model and the Langmuir isotherm model. The π-π stacking, hydrogen bond, and acid-base interactions were proposed to mainly account for the combination of the adsorbate and the adsorbent. Overall, these values indicated the high-performance biomass-derived carbon as a dye adsorbent and may boost the large-scale production and application of 3D hierarchical porous carbon with heteroatom doping in the field of wastewater treatment.

The design and synthesis of high efficiency adsorption materials for 1,3-propanediol: physical and chemical structure regulation

In this study, a series of polystyrene-divinylbenzene resins with precise physical structure regulation and chemical modification were successfully synthesized. The regulation of Friedel–Crafts reaction conditions resulted in several physical resins with various BET surface areas and pore structures, while the adsorption of 1,3-propanediol revealed that the molecular size and other physical properties exhibited a moderate contribution to the adsorption of hydrophilic compounds. The adsorption processes between 1,3-propanediol and nitrogen, oxygen and boron functional group modified resins were further explored, and boronic acid modified resins named PS-3NB and PS-SBT exhibited higher adsorption capacities than commercial resin CHA-111. The adsorption capacity of PS-3NB and PS-SBT reached 17.54 mg g⁻¹ and 17.23 mg g⁻¹, respectively, which were 37% and 35% higher than that of commercial resin CHA-111. Furthermore, the adsorption mechanism demonstrated that the content of boronic acid, solution pH and adsorbate hydrophobicity were the primary adsorption driving forces. Herein, we provided a method to modify polystyrene-divinylbenzene materials with boronic acid to selectively adsorb hydrophilic polyols via the specific affinity between boronic acid and diol molecule.

Chemically modified materials efficiently captured 1,3-propanediol via the specific affinity between boronic acid and diol.

Enhanced Cr(VI) removal by waste biomass derived nitrogen/oxygen co-doped microporous biocarbon

Herein, kitchen waste hydrolysis residue (KWHR) was utilized as the precursor to fabricate nitrogen/oxygen co-doped microporous biocarbons (NOMBs) with ultrahigh specific surface area via KOH activation. Activation temperature was found to be crucial for heteroatom doping and pore structure construction. Attractively, the obtained NOMB with high surface area (2417 m²/g) and microporosity (~ 90%) displayed an outstanding capacity of Cr(VI) removal (526.1 mg/g at pH 2). The kinetics and isotherm studies showed that the adsorption of Cr(VI) onto NOMB was well described by the pseudo-second-order kinetics and Langmuir isotherm. Moreover, it was found that Cr(VI) was partly reduced to Cr(III) during the removal process as the nitrogen/oxygen functionalities and unsaturated carbon bond played crucial roles of electron-donors, which revealed the fact that the removal of Cr(VI) by NOMB was attributed to the coupling of adsorption and reduction reaction. Overall, this study has demonstrated the possibility of preparing microporous biocarbons using KWHR as a renewable material and the resultant NOMB is of great potential to detoxify Cr(VI).