Synthesis of a ferric hydroxide-coated cellulose nanofiber hybrid for effective removal of phosphate from wastewater

Recent advances in nanocellulose-based adsorbent for sustainable removal of pharmaceutical contaminants from water bodies: A review

The long-term presence of pharmaceutical pollution in water bodies has raised public awareness. Nanocellulose is often used in adsorption to remove pollutants from wastewater since it is an abundant, green and sustainable material. This paper offers an extensive overview of the recent works reporting the potential of nanocellulose-based adsorbents to treat pharmaceutical wastewater. This study distinguishes itself by not only summarizing recent research findings but also critically integrating discussions on the improvements in nanocellulose production and sorts of alterations based on the type of pharmaceutical contaminants. Commonly, charged, or hydrophobic characteristics are introduced onto nanocellulose surfaces to accelerate and enhance the removal of pharmaceutical compounds. Although adsorbents based on nanocellulose have considerable potential, several significant challenges impede their practical application, particularly concerning cost and scalability. Large-scale synthesis of nanocellulose is technically challenging and expensive, which prevents its widespread use in wastewater treatment plants. Continued innovation in this area could lead to breakthroughs in the practical application of nanocellulose as a superior adsorbent. The prospects of utilization of nanocellulose are explained, providing a sustainable way to address the existing restriction and maximize the application of the modified nanocellulose in the field of pharmaceutical pollutants removal.

Sustainable adsorbent frameworks based on bio-resourced materials and biodegradable polymers in selective phosphate removal for waste-water remediation

Phosphorus to an optimum extent is an essential nutrient for all living organisms and its scarcity may cause food security, and environmental preservation issues vis-à-vis agroeconomic hurdles. Undesirably excess phosphorus intensifies the eutrophication problem in non-marine water bodies and disrupts the natural nutrient balance of the ecosystem. To overcome such dichotomy, biodegradable polymer-based adsorbents have emerged as a cost-effective and implementable approach in striking a "desired optimum-undesired excess" balance pertaining to phosphate in a sustainable manner. So far, the reports on adopting such adsorbent-approach for wastewater remediation remained largely scattered, unstructured, and poorly correlated. In this background, the contextual review comprehensively discusses the current state-of-the-art in utilizing biodegradable polymeric frameworks as an adsorbent system for phosphate removal and its efficient recovery from the aquatic ecosystem, while highlighting their characteristics-specific functional efficiency vis-à-vis easiness of synthetic and commercial viability. The overview further delves into the sources and environmental ramifications of excessive phosphorus in water bodies and associated mechanistic pathways of phosphorus removal via adsorption, precipitation, and membrane filtration enabled by biodegradable (natural and synthetic) polymeric substrates. Finally, functionality optimization, degradability tuning, and adsorption selectivity of biodegradable polymers are highlighted, while aiming to strike a balance in "removal-recovery-reuse" dynamics of phosphate. Thus, the current review not only paves the way for future exploration of biodegradable polymers in sustainable cost-effective adsorbents for phosphorus removal but also can serve as a guide for researchers dealing with this critical issue.

Cerium(IV) chitosan-based hydrogel composite for efficient adsorptive removal of phosphates(V) from aqueous solutions

The excess presence of phosphate(V) ions in the biosphere is one of the most serious problems that negatively affect aqueous biocenosis. Thus, phosphates(V) separation is considered to be important for sustainable development. In the presented study, an original cerium(IV)-modified chitosan-based hydrogel (Ce-CTS) was developed using the chemical co-precipitation method and then used as an adsorbent for efficient removal of phosphate(V) ions from their aqueous solutions. From the scientific point of view, it represents a completely new physicochemical system. It was found that the adsorptive removal of phosphate(V) anions by the Ce-CTS adsorbent exceeded 98% efficiency which is ca. 4-times higher compared with the chitosan-based hydrogel without any modification (non-cross-linked CTS). The best result of the adsorption capacity of phosphates(V) on the Ce-CTS adsorbent, equal to 71.6 mg/g, was a result of adsorption from a solution with an initial phosphate(V) concentration 9.76 mg/dm3 and pH 7, an adsorbent dose of 1 g/dm3, temperature 20 °C. The equilibrium interphase distribution data for the Ce-CTS adsorbent and aqueous solution of phosphates(V) agreed with the theoretical Redlich-Peterson and Hill adsorption isotherm models. From the kinetic point of view, the pseudo-second-order model explained the phosphates(V) adsorption rate for Ce-CTS adsorbent the best. The specific effect of porous structure of adsorbent influencing the diffusional mass transfer resistances was identified using Weber-Morris kinetic model. The thermodynamic study showed that the process was exothermic and the adsorption ran spontaneously. Modification of CTS with cerium(IV) resulted in the significant enhancement of the chitosan properties towards both physical adsorption (an increase of the point of zero charge of adsorbent), and chemical adsorption (through the presence of Ce(IV) that demonstrates a chemical affinity for phosphate(V) anions). The elaborated and experimentally verified highly effective adsorbent can be successfully applied to uptake phosphates(V) from aqueous systems. The Ce-CTS adsorbent is stable in the conditions of the adsorption process, no changes in the adsorbent structure or leaching of the inorganic filling were observed.

Fe-modified fly ash/cotton stalk biochar composites for efficient removal of phosphate in water: mechanisms and green-reuse potential

Excessive phosphate content input into natural water can lead to the waste of resource and eutrophication. Biochar is a kind of low-cost adsorbent. However, its adsorption capacity for phosphate is low. In order to solve this problem, Fe compound-modified fly ash/cotton stalk biochar composites (Fe-FBC) were prepared through co-pyrolyzed fly ash and cotton stalk at 800℃, followed by infiltration of FeSO₄ solution. The samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, and zeta potential. After modification, the hydrophilicity and polarity of Fe-FBC increased. In addition, the pore volume, specific surface area, and surface functional groups were significantly improved. The adsorption behavior of Fe-FBC for the removal of phosphate from water can be well fitted by the pseudo-second-order kinetic and Sips isotherm adsorption model, with a maximum adsorption capacity of 47.91 mg/g. Fe-FBC maintained a high adsorption capacity in the pH range of 3-10. The coexisting anions (NO₃^-, SO₄^2-, and Cl^-) had negligible effects on phosphate adsorption. The adsorption mechanisms of Fe-FBC include electrostatic attraction, ligand exchange, surface complexation, ion exchange, chemical precipitation, and hydrogen bonding. Moreover, the desorption process of phosphate was investigated, indicating that the phosphate-saturated Fe-FBC could use as slow-release phosphate fertilizer. This study proposed a potentially environmental protection and recycling economy approach, which consists of recycling resources and treating wastes with wastes.

A biomimetic nanoplatform for precise reprogramming of tumor-associated macrophages and NIR-II mediated antitumor immune activation

The therapeutic effects of photothermal therapy (PTT) are dependent on the photothermal conversion efficiency of photothermal agents (PTAs) in tumors and the subsequent activation of the antitumor immune system. However, the insufficient tumor accumulation of current PTAs and the inevitable recruitment of tumor-associated macrophages (TAMs) could further compromise the antitumor activities of PTT. To address these issues, a biomimetic photothermal nanoplatform Au@Fe-PM is developed for the targeted remodeling of TAMs, which promotes the antitumor immunity of PTT. Au nanorods with second near-infrared (NIR-II) absorptions are fabricated to serve as PTAs to induce immunogenic cell death in tumor cells. The ferric hydroxide shell coated on Au nanorods can release iron ions to repolarize M2-like TAMs into the tumoricidal M1 phenotype via P38 and STAT1-mediated signaling pathways. Moreover, the surface decoration of platelet membranes endows biomimetic nanoplatform with enhanced tumor targeting ability for precise tumor ablation and TAM regulation. Consequently, Au@Fe-PM under NIR-II laser irradiation exhibits significantly higher inhibitory effects in a poor immunogenic 4T1 tumor-bearing mouse model with a 50% complete remission rate compared to conventional PTT (0%). By simultaneously reversing the immunosuppressive tumor microenvironment, this biomimetic nanoplatform offers a promising strategy for enhancing the antitumor efficacy of PTT. STATEMENT OF SIGNIFICANCE: The therapeutic effects of current photothermal therapy (PTT) are hindered by the insufficient tumor accumulation of conventional photothermal agents and the recruitment of immunosuppressive tumor-associated macrophages (TAMs) after PTT. Herein, we report a biomimetic iron-based second near-infrared (NIR-II) photothermal nanoplatform (Au@Fe-PM) for targeted TAMs reprogramming and NIR-II mediated anti-tumor immunity. Au@Fe-PM can actively target the tumor site with the help of surface-decorated platelet membranes. Meanwhile, iron ions would be released from Au@Fe-PM in acidic lysosomes to reprogram TAMs into tumoricidal M1-like macrophages, which promotes the antitumor responses elicited by NIR-II PTT, thereby contributing to remarkable tumor inhibitory effects, with 50% higher complete remission rate than that of conventional PTT.

Effective Thallium(I) Removal by Nanocellulose Bioadsorbent Prepared by Nitro-Oxidation of Sorghum Stalks

Thallium(I) (Tl(I)) pollution has become a pressing environmental issue due to its harmful effect on human health and aquatic life. Effective technology to remove Tl(I) ions from drinking water can offer immediate societal benefits especially in the developing countries. In this study, a bio-adsorbent system based on nitro-oxidized nanocellulose (NOCNF) extracted from sorghum stalks was shown to be a highly effective Tl(I) removal medium. The nitro-oxidation process (NOP) is an energy-efficient, zero-waste approach that can extract nanocellulose from any lignocellulosic feedstock, where the effluent can be neutralized directly into a fertilizer without the need for post-treatment. The demonstrated NOCNF adsorbent exhibited high Tl(I) removal efficiency (>90% at concentration < 500 ppm) and high maximum removal capacity (Qm = 1898 mg/g using the Langmuir model). The Tl(I) adsorption mechanism by NOCNF was investigated by thorough characterization of NOCNF-Tl floc samples using spectroscopic (FTIR), diffraction (WAXD), microscopic (SEM, TEM, and AFM) and zeta-potential techniques. The results indicate that adsorption occurs mainly due to electrostatic attraction between cationic Tl(I) ions and anionic carboxylate groups on NOCNF, where the adsorbed Tl(I) sites become nuclei for the growth of thallium oxide nanocrystals at high Tl(I) concentrations. The mineralization process enhances the Tl(I) removal efficiency, and the mechanism is consistent with the isotherm data analysis using the Freundlich model.

Synchronous N and P Removal in Carbon-Coated Nanoscale Zerovalent Iron Autotrophic Denitrification─The Synergy of the Carbon Shell and P Removal

Fe⁰ is a promising electron donor for autotrophic denitrification in the simultaneous removal of nitrate and phosphorus in low C/N wastewater. However, P removal may inevitably inhibit bio-denitrification. It has not been well recognized and led to an overdose of iron materials. This study employed carbon-coated zerovalent iron (Fe⁰@C) to support autotrophic denitrification to mitigate the inhibition effects of P removal and enhance both N and P removal. The critical role of the carbon shell in Fe⁰@C was to block the direct contact between Fe⁰ and P and NO₃^--N, to maintain the Fe⁰ activity. Besides, P inhibited the chemical reduction of NO₃^--N by competing for Fe⁰ active sites. This indirectly boosted H₂ generation and promoted bio-denitrification. P removal displayed negligible effects on microbial species but indirectly enhanced the nitrogen metabolic activities because of promoted H₂ in Fe⁰@C-based autotrophic denitrification. Bio-denitrification, in turn, strengthened Fe-P co-precipitation by promoting the formation of ferric hydroxide as a secondary adsorbent for P removal. This study demonstrated an efficient method for simultaneous N and P removal in autotrophic denitrification and revealed the synergistic interactions among N and P removal processes.

Preparation of Fe-filled MOF-Al-based hydrogel for efficient reclaim of phosphate from wastewater and reusing as a slow-release fertilizer

In this study, a novel Fe-filled MOF-Al-based hydrogel (SA@Fe@MOF-Al) was prepared and characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis. The SA@Fe@MOF-Al hydrogel bead was used as an adsorbent to adsorb H2PO4- from wastewater. The effects on adsorption were investigated, including pH and coexist ion. The adsorption reached equilibrium within 30 min. The maximum H2PO4- adsorption capacity of SA@Fe@MOF-Al was 103.09 mg g^-1 at 298K with pH 7.0. Meanwhile, thermodynamic results confirmed that adsorption is exothermic and spontaneous. The adsorption kinetics displayed that SA@Fe@MOF-Al adsorption process was suitable to the pseudo-first-order and Langmuir model. Moreover, the feasibility of reusing the P-laden carrier material as a slow-release fertilizer was determined. The study results indicated that the product demonstrated excellent slow-release and water-retention properties. Thus, it has potential applications in improving soil moisture content and reducing soil moisture evaporation rate.

Phosphate removal and recovery by lanthanum-based adsorbents: A review for current advances

Controlling eutrophication and recovering phosphate from water bodies are hot issues in the 21st century. Adsorption is considered to be the best method for phosphate removal because of its high adsorption efficiency and fast removal rate. Among the many adsorbents, lanthanum (La)-based adsorbents have been paid more and more attention due to their strong affinity to phosphorus. This paper reviews research of phosphate adsorption on La-based adsorbents in different La forms, including lanthanum oxide/hydroxide, lanthanum mixed metal oxide/hydroxide, lanthanum carbonate, La³⁺, La-based metal-organic framework (La-MOF) and La-MOF derivatives. The La-based adsorbents can be loaded on many carriers, such as carbon material, clay minerals, porous silica, polymers, industrial wastes, and others. We find that lanthanum oxide/hydroxide and La³⁺ adsorbents are mostly studied, while those in the forms of lanthanum carbonate, La-MOF, and La-MOF derivatives are relatively few. The kinetic process of most phosphate adsorption is pseudo-second-order and the isotherm process is in accordance with the Langmuir model. The cost of La-based and other traditional adsorbents was compared. The adsorption mechanisms are categorized as electrostatic attraction, ligand exchange, Lewis acid-base interaction, ion exchange and surface precipitation. Besides, regeneration methods of La-based adsorbents are mainly acid, alkali, and salt-alkali. In addition, the La-based adsorbents after absorbing phosphate can be directly used as a slow-release fertilizer. This review provides a basis for the research on phosphate adsorption by La-based adsorbents. It should be carried out to further develop La-based materials with high adsorption capacity and good regeneration ability. Meanwhile, studies have been conducted on the reuse of phosphate after desorption, which needs more attention in future research.

Mutual-activation between Zero-Valent iron and graphitic carbon for Cr(VI) Removal: Mechanism and inhibition of inherent Side-reaction

The low reactivity of zero-valent iron (ZVI) usually limits its application for pollutant remediation. Therefore, a microscopic galvanic cell (mGC) with short-circuited cathode and anode was synthesized to intensify its galvanic corrosion. The prepared mGC exhibited 7.14 times higher Fe(II) release performance than ordinary nanoscale-ZVI (nZVI), rendering efficient Cr(VI) removal performance. Density functional theory (DFT) revealed mutual-activation of the cathode and anode due to close proximity, dramatically enhancing the galvanic corrosion of Fe(0) in mGC. The corrosion potential of mGC was measured as -0.77 V, which was 100 mV more negative than nZVI. The released electrons and surface-bond Fe(II) from anode in mGC was proved to be the dominant reductive species. More importantly, Cr(VI) reduction was slightly inhibited by hydroxyl radicals generated by a series of inherent side-reactions in the system, which could be well eliminated by low concentrations of 4-acetamido phenol. This study provides a promising strategy for ZVI activation, and sheds light on its environmental applications.

Three-dimensional macroscopic aminosilylated nanocellulose aerogels as sustainable bio-adsorbents for the effective removal of heavy metal ions

Designing an environmentally benign bio-adsorbent for the removal of heavy metal ions from aqueous medium was a sustainable strategy to ensure water safety. Herein, three-dimensional macroscopic aminosilyated nanocellulose aerogels (APTM_S-modified TO-NFC) for the removal of heavy metal ions in water were successfully synthesized from bamboo-derived TEMPO-oxidized nanofibrillated cellulose (TO-NFC) and aminopropyltrimethoxysilane (APTMs) via a facile freeze-drying process. Owing to a relatively high BET surface area (129.32 m² g^-1), high porosity (99.14%) as well as high substitution degree of amino groups (0.41), the resulting APTM_S-modified TO-NFC aerogel exhibited good adsorption capacity of 99.0, 124.5, and 242.1 mg g^-1 for Cu²⁺, Cd²⁺ and Hg²⁺, respectively. Furthermore, the crosslinked and three-dimensionally porous architecture imparted it with relatively high compression strength, good excellent stability in water, and ease of recyclability from water after the usage. The pH value of the solution had a great influence on adsorption efficiency of the aerogel adsorbent, and optimal adsorption efficiency could be achieved at pH 3-7. Thermodynamic parameters suggested the spontaneous and endothermic nature of adsorption process. This work provides a facile method for preparing sustainable bio-adsorbent for effective heavy metal ions removal from aqueous medium.

Recent Advances in the Fabrication and Environmental Science Applications of Cellulose Nanofibril-Based Functional Materials

Cellulose is one of the important biomass materials in nature and has shown wide applications in various fields from materials science, biomedicine, tissue engineering, wearable devices, energy, and environmental science, as well as many others. Due to their one-dimensional nanostructure, high specific surface area, excellent biodegradability, low cost, and high sustainability, cellulose nanofibrils/nanofibers (CNFs) have been widely used for environmental science applications in the last years. In this review, we summarize the advance in the design, synthesis, and water purification applications of CNF-based functional nanomaterials. To achieve this aim, we firstly introduce the synthesis and functionalization of CNFs, which are further extended for the formation of CNF hybrid materials by combining with other functional nanoscale building blocks, such as polymers, biomolecules, nanoparticles, carbon nanotubes, and two-dimensional (2D) materials. Then, the fabrication methods of CNF-based 2D membranes/films, three-dimensional (3D) hydrogels, and 3D aerogels are presented. Regarding the environmental science applications, CNF-based nanomaterials for the removal of metal ions, anions, organic dyes, oils, and bio-contents are demonstrated and discussed in detail. Finally, the challenges and outlooks in this promising research field are discussed. It is expected that this topical review will guide and inspire the design and fabrication of CNF-based novel nanomaterials with high sustainability for practical applications.

Treatment of hazardous wastewater generated from metal finishing and electro-coating industry via self-coagulation: Case study

The aim of this study is to find out a sustainable and cost-effective solution to manage hazardous shock loads from metal finishing and electro-coating industry. Results indicated that the main sources of hazardous wastewater are coming from batch chemical cleaning of degreasing basin (CCDB) (pH 13) and contains very hazardous chemicals, batch chemical cleaning of phosphating basin (CCPB) (pH 1.03) and contains high concentrations of iron (2300 mg/L) and zinc (2400 mg/L) and degreasing basin contents (DBC). Different treatment approaches were investigated. Results indicated that mixing CCDB with CCPB at their actual discharge allowed to form a self-coagulant of metal hydroxide which was utilized to treat the (DBC) followed by sedimentation. Removal efficiency of COD (87%), TSS (94%), and oil and grease (92%) were achieved. To compare the efficiency of this treatment approach, conventional chemical coagulation of DBC was carried out using FeCl₃ but the amount was very high. In conclusion, results proved the advantage of using self-coagulation to treat DBC since it eliminates the use of external chemicals and provides an integrated solution for the three main sources of hazardous pollutants. PRACTITIONER POINTS: The manuscript provide an innovative and sustainable solution to the shock loads of hazardous wastewater generated from metal finishing and E-coating industry by utilizing iron-rich wastewater from chemical cleaning of phosphating basin and alkaline wastewater from chemical cleaning of degreasing basin to produce metal hydroxide. The metal hydroxide was cost-effective and technically effectively than external coagulant in treating highly polluted degreasing basin content at due discharge time. Iron-rich wastewater could be used to produce self-coagulant of iron hydroxide. Mixing iron rich wastewater and alkaline wastewater produce iron hydroxide. Iron hydroxide is cost-effective in treating hazardous wastewater of degreasing basin.

Effective removal of tetracycline antibiotics from wastewater using practically applicable iron(III)-loaded cellulose nanofibres

The non-toxic and completely biodegradable cellulose within bamboo is one of the most abundant agricultural polysaccharide wastes worldwide, and can be processed into cellulose nanofibres (CNFs). Iron(III)-loaded CNFs (Fe(III)@CNFs) derived from bamboo were prepared to improve the adsorption of tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC) from an aqueous solution. The preparation conditions of Fe(III)@CNFs suitable for the simultaneous adsorption of three tetracycline antibiotics (TCs) were investigated. Various analyses proved the abundance of oxygen-containing functional groups and the existence of Fe(III) active metal sites in Fe(III)@CNFs. In batch experiments, Fe(III)@CNFs were applied under a wide pH range and the maximum adsorption capacities were 294.12, 232.56 and 500.00 mg g-1 (for TC, CTC and OTC, respectively). In addition, different concentrations and types of coexisting anions have a weak effect on TCs adsorption. The original TCs adsorption capacities of Fe(III)@CNFs remained stable (greater than 92%) after five cycles when UV + H2O2 was used as the regeneration method. Four adsorption mechanisms (surface complexation, hydrogen bonding, electrostatic interaction and van der Waals force) were obtained for the endothermic adsorption of TCs, among which surface complexation between Fe(III) and TCs always dominates. The practically applicable Fe(III)@CNFs adsorbents are promising for TCs enrichment and remediation in engineering applications.

Phosphorus immobilization in water and sediment using iron-based materials: A review

As an essential element for life, phosphorus (P) is very important for organisms. However, excessive P in water and sediment can cause eutrophication, which poses a potential risk to drinking water safety and the sustainability of aquatic ecosystems. Therefore, effective phosphorus-control in water and sediment is the key strategy to control eutrophication. Iron-based materials exhibit high efficiency for P immobilization due to their strong affinity with P, low cost, easy availability, and environmentally friendliness. They are promising materials for controlling P in application. This work comprehensively summarizes the recent advances on P immobilization in water and sediment by different iron-based materials, including iron (hydr)oxides, iron salts, zero-valent iron and iron-loaded materials. This review is focused on the mechanism of the processes and how they are impacted by major influencing factors. The combination of iron-containing materials with other assisting materials is a good strategy to enhance P-fixation efficiency and selectivity. Finally, the current challenges and prospects of P-control technologies based on iron-containing materials are proposed. This review provides a systemic theoretical and experimental foundation for P-immobilization in water and sediment using iron-based materials.

Preparation of TiO2/cellulose nanocomposites as antibacterial bio-adsorbents for effective phosphate removal from aqueous medium

The design of environmentally benign bio-adsorbents for the removal of phosphate from aqueous medium was an economic and effective way for controlling eutrophication. Herein, we prepared three kinds of TiO₂/cellulose (CE-Ti) nanocomposites by a facile hydrolysis-precipitation method, and used them as antibacterial bio-adsorbents for the removal of phosphate from aqueous medium. Multiple techniques including Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and thermogravimetric analysis (TGA) were employed to characterize the nanostructure and characteristics of the prepared CE-Ti nanocomposite. The adsorption capacity of the CE-Ti was 19.57 mg P g^-1 according to the Langmuir model, which was 6 times higher than that of CE. Importantly, the bacterial inhibition zone of the CE-Ti was 2.88 mm (that of CE was 0 mm), indicating that CE-Ti had good antibacterial activity that could reduce the attachment of the microorganism to the surface of CE-Ti, which was suitable for long-term phosphate removal. Moreover, the CE-Ti had good adsorption selectivity and anti-interference capability, according to interfering ions and ion strength experiments. Furthermore, Ti⁴⁺ leakage tests suggested that CE-Ti was highly stable under acidic, neutral and alkali conditions. These results indicated that the CE-Ti nanocomposite could be utilized as a promising antibacterial bio-adsorbent for effective phosphate removal from aqueous medium.

Enhanced removal of Co(II) and Ni(II) from high-salinity aqueous solution using reductive self-assembly of three-dimensional magnetic fungal hyphal/graphene oxide nanofibers

Layer-structured graphene oxide excellent carrier for modifications; however, its poor recoverability and stability preclude its application in wastewater treatment fields. Herein, three-dimensional magnetic fungal hyphal/graphene oxide nanofibers (MFHGs) were assembled by a reductive self-assembly (RSA) strategy for the efficient capture of Co(II) and Ni(II) from high-salinity aqueous solution. The RSA strategy is inexpensive, eco-friendly and easy to scale up. The obtained MFHGs enhanced the dispersity and stability of graphene oxide and exhibited excellent magnetization and large coercivity, leading to satisfactory solid-liquid separation performance and denser sediment. The results of batch removal experiments showed that the maximum removal capacity of MFHGs for Ni(II) and Co(II) was 97.44 and 104.34 mg/g, respectively, in 2 g/L Na₂SO₄ aqueous solution with a pH of 6.0 at 323 K, and the effects of initial pH and ionic strength on Co(II) and Ni(II) removal were explored. Yield residue analysis indicated that the high porosity and oxygen-containing functional groups of MFHGs remarkably improved their Co(II)- and Ni(II)-removal capacities. According to the analysis, hydroxyl groups and amine groups participated in the chemical reaction of Co(II) and Ni(II) removal, and cation-exchange chemical adsorption was dominant during the Co(II)- and Ni(II)-removal process. Based on the attributes of MFHGs, a continuous-flow recycle reactor (CFRR) was proposed for emergency aqueous solution treatment and exhibited satisfactory removal efficiency and regeneration performance. The combination of MFHGs and the proposed CFRR is a promising water treatment strategy for rapid treatment applications.

Reusable Hyperbranched Polyethylenimine-Functionalized Ethyl Cellulose Film for the Removal of Phosphate with Easy Separation

The design of a reusable film adsorbent with easy solid-liquid separation for the removal of phosphate is necessary and significant but remains hugely challenging. Herein, the hyperbranched polyethylenimine-functionalized ethyl cellulose (HPEI-EC) film was successfully synthesized by a one-step solution-casting method. The structure and elemental composition of the HPEI-EC film were characterized by Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The phosphate adsorption capacity of the HPEI-EC film was 15.53 mg g-1, which is 12 times higher than that of EC. Significantly, the elongation at break of the HPEI-EC film was 13.43%, which is higher than that of the EC film (8.9%), and the HPEI-EC film had a considerable tensile strength of 13.21 MPa. Such good mechanical properties of the HPEI-EC film bring about the advantage of the saturated HPEI-EC film, allowing it to be easily taken out using a pair of tweezers, which significantly reduces the operation time and saves the cost in the application process. Furthermore, the HPEI-EC film possessed good reusability, and 71.6% of the original adsorption capacity of phosphate was retained even after five cycles. Moreover, the electrostatic interaction between protonated the amine group (-NH3 +) and the phosphate ion (PO4 3-) is mainly responsible for the adsorption process. This study presents a low-cost and reusable film adsorbent for the effective removal of phosphate from water and provides an easy solid-liquid separation method for use in the adsorption field.

Insight into efficient phosphorus removal/recovery from enhanced methane production of waste activated sludge with chitosan-Fe supplementation

Fe(III)-loaded chitosan (CTS-Fe) composite was used for the first time to remove and recover phosphorus (P) from waste activated sludge (WAS) via anaerobic digestion (AD). The P transformation pathway and the effect of CTS-Fe addition on the AD process were investigated using batch experiments. The P fractionation results indicate that non-apatite inorganic phosphorus (NAIP) reduction in the solid phase of sludge at 20 g/L of CTS-Fe addition (6.72 mg/g-SS) was 2.4 times higher than that in the control (2.77 mg/g-SS, no CTS-Fe addition). This is probably brought about by the added CTS-Fe enhanced the reduction of Fe(III)-P compounds in the sludge with phosphate released into the liquid phase. CTS-Fe can efficiently recover 95% of P from the liquid digestate of WAS. Notably, partial Fe(III) on the CTS-Fe was reduced and effectively combined with P to form vivianite crystals on the CTS-Fe surface during the AD process. Characterization analysis demonstrated that ligand exchange and chemical precipitation were the dominant mechanisms for P removal/recovery. Furthermore, the addition of CTS-Fe increased methane production by 11.9 - 32.2% under the tested conditions, likely attributable to the enhanced hydrolysis of WAS under CTS-Fe supplementation. As the P-loaded CTS-Fe particles can be easily separated and recovered from the AD system and further reutilized in agriculture, this study could provide a new approach for simultaneous P removal/recovery and enhanced methane production from AD of WAS.

Highly efficient removal of p-arsanilic acid with Fe(II)/peroxydisulfate under near-neutral conditions

As a common animal feed additive, p-arsanilic acid (p-AsA) is thought to be excreted with little uptake and unchanged chemical structure, threatening the environment by potentially releasing more toxic inorganic arsenic. We herein investigated the removal of arsenic by in situ formed ferric (oxyhydr)oxides with the promotion of p-AsA degradation in Fe(II)/peroxydisulfate (PDS) system. Results showed that under acid conditions, p-AsA degraded very quickly and over 99% of p-AsA (5 μM) was degraded within 10 min at the optimal dosage of Fe(II) (100 μM) and PDS (150 μM) at pH 3, while less than 66.4% of arsenic was removed at pH 3-5. Higher pH (3-7) would inhibit the degradation of p-AsA but promote the arsenic removal. At pH 6-7, over 98.5% of total arsenic was removed, while the degradation efficiency of p-AsA was lower than 52.4%. HPLC-ICP-MS results indicated that the arsenic group was cleaved from p-AsA in the form of As(III) and then rapidly oxidized to As(V). FTIR and XPS analysis indicated that both As(V) products and residual p-AsA were bonded to ferric (oxyhydr)oxides via hydroxyl groups. Common cations (e.g., Na⁺, Ca²⁺, Mg²⁺) and anions such as Cl^-, SO₄^2-, CO₃^2- had no significant influence on arsenic removal, while SiO₃^2-, PO₄^3- and HA inhibited the removal of total arsenic, mainly by affecting the zeta potential of iron particles. In summary, the Fe(II)/PDS process, as an efficient method for partial oxidation and simultaneous adsorption of p-AsA under near-neutral conditions, is expected to control the potential environmental risks of p-AsA.

Selective and efficient sequestration of phosphate from waters using reusable nano-Zr(IV) oxide impregnated agricultural residue anion exchanger

There is an urgent need to develop low-cost and effective adsorbents for enhanced removal of phosphate from contaminated waters. In this study, nanosized Zr(IV) oxide particles were immobilized on the amino modified corn staw (MCS) to fabricate a novel nanocomposite (Zr@MCS) with superior application capability. Compared with the widely used commercial anion exchangers in previous studies, the modified agricultural residue was empolyed as the host to avoid the high costs and secondary pollution in the preparation. Zr@MCS displayed remarkable selective removal of phosphate from water even in the presence of coexisting anions (Cl^-, SO₄^2-, NO₃^-) at high levels, as well as with a high adsorption capacity, fast adsorption kinetics and high availability in the wide range of pH 2-8 toward phosphate. The excellent adsorption performance of Zr@MCS is attributed to the synergistic effect of the electrostatic attraction of the quaternary ammonium groups fixed on the host skeleton and the specific adsorption of phosphate derived from the hydroxyl functional groups of Zr(IV) oxide. The exhausted Zr@MCS can be effectively regenerated by 5% NaOH-NaCl solution for sustainably utilized, and phosphorus in the desorption effluent could be recovered as high-quality struvite by a simple struvite recovery process. Furthermore, the considerable treatment volume for the synthetic solution and real wastewater in a fixed-bed flow system indicated that Zr@MCS is of great potential for phosphate removal in practice.

Cerium oxide nanoparticle functionalized lignin as a nano-biosorbent for efficient phosphate removal

An inexpensive, high stability, and good reusability nano-biosorbent L-NH₂@Ce for efficient phosphate removal was fabricated by a facile method.

Arsenic(III) Removal by Nanostructured Dialdehyde Cellulose-Cysteine Microscale and Nanoscale Fibers

Arsenite (As(III)) contamination in drinking water has become a worldwide problem in recent years, which leads to development of various As(III) remediation approaches. In this study, two biomass-based nanostructured materials, microscale dialdehyde cellulose-cysteine (MDAC-cys) and nanoscale dialdehyde cellulose-cysteine (NDAC-cys) fibers, have been prepared from wood pulp. Their As(III) removal efficiencies and mechanism were determined by combined adsorption, atomic fluorescence spectrometry, microscopy (scanning electron microscopy, transmission electron microscopy, and atomic force microscopy), and spectroscopy (Fourier transform infrared, 13C CPMAS NMR) methods. The adsorption results of these materials could be well described by the Freundlich isotherm model, where the maximum adsorption capacities estimated by the Langmuir isotherm model were 344.82 mg/g for MDAC-cys and 357.14 mg/g for NDAC-cys, respectively. Both MDAC-cys and NDAC-cys materials were further characterized by X-ray diffraction and thermogravimetric analysis, where the results indicated that the thiol groups (the S content in MDAC-cys was 12.70 and NDAC-cys was 17.15%) on cysteine were primarily responsible for the adsorption process. The nanostructured MDAC-cys system appeared to be more suitable for practical applications because of its high cost-effectiveness.

Preparation and regeneration of iron-modified nanofibres for low-concentration phosphorus-containing wastewater treatment

In this study, nanocellulose (CNFs) was prepared by a mechanical shearing method, a simple and pollution-free process. Iron hydroxide was loaded on nanocellulose, a natural macromolecule derived from bamboo, to produce the second-generation iron-loaded nanocellulose for the removal of low-concentration phosphorus from wastewater. We found that the best modified ferric salt was ferric chloride. When the mass ratio of Fe(OH)3 and CNFs was 1.5 : 1, freeze-drying with liquid nitrogen yielded the best adsorption performance. The adsorption process of Fe(OH)3@CNFs followed the pseudo-second-order kinetics and belonged to chemical adsorption. Regeneration experiments showed that after 10 cycles of adsorption-regenerations of the adsorbent, the phosphorus adsorption efficiency was still stable at 80% of the initial material. The prepared adsorbent was characterized by the BET surface area measurement, scanning electron microscopy and FT-IR. The surface morphology, pore size and elements of materials before and after iron loading were analysed. Compared with other adsorbents, the phosphorus removal performances of the second-generation iron-loaded nanocellulose were superior. Compared with the first-generation material, the second-generation adsorbent is simpler and more environmentally friendly.

Phosphate adsorption from wastewater using ZnAl-LDO-loaded modified banana straw biochar

ZnAl-layered double hydroxide-loaded banana straw biochar (ZnAl-LDH-BSB) was prepared via the hydrothermal method, and the efficient phosphorus removal agent ZnAl-LDO-BSB was obtained by calcination at 500 °C. Based on the ZnAl-LDO-BSB adsorption characteristics, the adsorption mechanism was evaluated via TG/DTA, FTIR, XRD, SEM, HRTEM, and other characterization methods. The results showed that the ZnAl-LDO-BSB assembled into microspheres with typical hexagonal lamellar structures and presented good thermal stability. The adsorption of total phosphate (TP) by ZnAl-LDO-BSB conforms to the Langmuir model, and the theoretical maximum adsorption capacity is 185.19 mg g^-1. The adsorption kinetics were in accordance with the second-order kinetic model, and the anion influence on TP adsorption followed the order CO₃^2- > SO₄^2- > NO₃^-. The combination of zeta potential measurements with the FTIR, XRD, SEM, HRTEM, and XPS results suggested that ZnAl-LDO-BSB adsorbs TP mainly by electrostatic adsorption, surface coordination, and anion intercalation. Graphical abstract.

Characteristics of nitrogen and phosphorus adsorption by Mg-loaded biochar from different feedstocks

Herein, biochars from 6 different feedstocks (taro straw, corn straw, cassava straw, Chinese fir straw, banana straw, and Camellia oleifera shell) were produced using magnesium chloride (MgCl₂) as a modifier due to their sorption behavior toward NH₄⁺-N and phosphorus in an aqueous solution. The biochar characteristics were evaluated, including pH, pH_PZC, biochar magnesium content, and total pore volume (PV_tot). The experimental results in terms of the kinetics and equilibrium isotherms showed that the cassava straw and banana straw biochars exhibited the theoretical maximum saturated adsorption capacities of 24.04 mg·g^-1 (NH₄⁺-N) and 31.15 mg·g^-1 (TP), respectively. Biochar produced from these feedstocks had higher magnesium contents and greater total pore volumes, reflecting the significant contributions from magnesium and steric effects. FTIR, XRD, and SEM/EDS analyses demonstrated that NH₄⁺-N and TP sorption mechanisms predominantly involved surface electrostatic attraction, Mg²⁺ precipitates and complexation with surface hydroxyl functional groups.

Optimization and mechanism studies on cell disruption and phosphorus recovery from microalgae with magnesium modified hydrochar in assisted hydrothermal system

Considering the phosphorus (P) reserve state and its value, recovery of P from microalgae has become a popular topic. In this study, an integrated system of a hydrothermal process for microalgae cell disruption to release P and magnesium modified hydrochar adsorption to capture P was set up. Emission scanning electron microscopy with Energy Dispersive X-ray spectroscopy and Three-Dimensional Excitation Emission matrix spectroscopy with parallel factor analysis were applied to evaluate the P release process from microalgae and found the optimal breaking-wall condition (P release 90.5%, hydrothermal digestion mixture of H₂O₂ and NaOH at 348 K). Parallel factor analysis showed there was a close relationship between P and humic-like substance. Hydrochar loaded with magnesium exhibited a strong affinity for P, with maximum capacity 89.61 mg/g at 318 K. The P adsorption fitted pseudo-second-order kinetic and Langmuir models. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were applied to reveal the mechanism of hydrochar modification and adsorption. It showed that Mg is loaded on the surface of hydrochar by electrostatic attraction and electron transfer with the carboxylic acid. P absorption was reached through anion exchange.

A green method to synthesize flowerlike Fe(OH)3 microspheres for enhanced adsorption performance toward organic and heavy metal pollutants

Dyestuffs and heavy metal ions in water are seriously harmful to the ecological environment and human health. Three-dimensional (3D) flowerlike Fe(OH)₃ microspheres were synthesized through a green yet low-cost injection method, for the removal of organic dyes and heavy metal ions. The Fe(OH)₃ microspheres were characterized by thermal gravimetric analysis (TGA), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) techniques. The adsorption kinetics of Congo Red (CR) on Fe(OH)₃ microspheres obeyed the pseudo-second-order model. Cr⁶⁺ and Pb²⁺ adsorption behaviors on Fe(OH)₃ microspheres followed the Langmuir isotherm model. The maximum adsorption capacities of the synthesized Fe(OH)₃ were 308, 52.94, and 75.64mg/g for CR, Cr⁶⁺, and Pb²⁺ respectively. The enhanced adsorption performance originated from its surface properties and large specific surface area of 250m²/g. The microspheres also have excellent adsorption stability and recyclability. Another merit of the Fe(OH)₃ material is that it also acts as a Fenton-like catalyst. These twin functionalities (both as adsorbent and Fenton-like catalyst) give the synthesized Fe(OH)₃ microspheres great potential in the field of water treatment.

Iron-loaded Sphagnum moss extract residue for phosphate removal

Sphagnum moss extract residue (SMER), obtained after pressurized hot water extraction, was modified with Fe(III) and investigated for phosphate sorption. Although moss extract contains value-added compounds, SMER is considered to be waste until suitable uses can be developed. The effect of modification conditions were investigated, i.e. different initial Fe(III) concentrations (0.024, 0.048 and 0.072 mol/L Fe³⁺) and modification pH values (5, 7 and 9). A modification pH of 5 and the highest initial Fe(III) concentration (0.072 mol/L Fe³⁺) resulted in the highest phosphate removal efficiency, and thus was selected for further study. The removal efficiency was found to decrease with increasing pH in the range of 3-9. Maximum removal efficiency (82%) for phosphate sorption was observed at pH 3 after 24 h contact time (dosage 2 g/L, initial concentration 15 mg P/L). With increased contact time, the phosphate removal efficiency improved and reached equilibrium within 48 h. The Elovich model was found to provide the best fit to the kinetic data. A capacity of 9-13 mg P/g was obtained with a 24-h contact time at pH 4. A good fit was achieved with the Redlich-Peterson equation. FTIR analysis confirmed that carboxylic acid groups were involved in the modification process. X-ray diffraction analyses showed that amorphous two-line ferrihydrite was precipitated onto SMER, which was supported by X-ray photoelectron spectroscopy analyses.

Investigation on mechanism of phosphate removal on carbonized sludge adsorbent

For the removal of phosphate (PO₄^3-) from water, an adsorbent was prepared via carbonization of sewage sludge from a wastewater treatment plant: carbonized sludge adsorbent (CSA). The mechanism of phosphate removal was determined after studying the structure and chemical properties of the CSA and its influence on phosphate removal. The results demonstrate that phosphate adsorption by the CSA can be fitted with the pseudo second-order kinetics and Langmuir isotherm models, indicating that the adsorption is single molecular layer adsorption dominated by chemical reaction. The active sites binding phosphate on the surface are composed of mineral particles containing Si/Ca/Al/Fe. The mineral containing Ca, calcite, is the main factor responsible for phosphate removal. The phosphate removal mechanism is a complex process including crystallization via the interaction between Ca²⁺ and PO₄^3-; formation of precipitates of Ca²⁺, Al³⁺, and PO₄^3-; and adsorption of PO₄^3- on some recalcitrant oxides composed of Si/Al/Fe.

A feasible approach to dispose of soil washing wastes: adsorptive removal of chlorobenzene compounds in aqueous solutions using humic acid modified with monoolein (HA–M)

Humic acid (HA), one of most ubiquitous natural resources in the world, was modified with monoolein to prepare a novel hydrophobic adsorbent (HA–M) for removal of chlorobenzene compounds (CBs) from aqueous solutions.