Ultrarapid and Sustainable Synthesis of Trimetallic-Based MOF (CrNiFe-MOF) from Stainless Steel and Disodium Terephthalate-Derived PET Wastes

Designing easy and sustainable strategies for the synthesis of metal-organic frameworks (MOFs) from organic and inorganic wastes with the efficient removal of phosphate from water remains a challenge. The majority of the reported works have utilized costly precursors and nonsoluble ligands for the synthesis of MOFs. Herein, we have developed a low-cost, simple, and sustainable alternative approach using the coprecipitation method in water at room temperature for the synthesis of a new adsorbent-based trimetallic MOF. Poly(ethylene terephthalate) and stainless steel wastes were used as sources of water-soluble disodium terephthalate ligand and three metallic species (chromium, nickel, and iron salts) for the fabrication of trimetallic MOF (CrNiFe-MOF), respectively. The newly developed MOF demonstrates a superior space-time yield of 5760 g m-3 day-1, reaching a level allowing the industrialization production of this sustainable MOF. The scanning electron microscopy and adsorption studies revealed that the developed trimetallic MOF consists of aggregated nanoparticles and the presence of defective as well as mesoporous structures. This MOF showed an enhanced adsorption capacity of phosphate from real eutrophic water samples and higher stability in a range of pHs. The density functional theory calculations evidenced that the phosphate ions preferentially adsorb over H2O toward the metal oxo-trimers, with the adsorption energies increasing from H3PO4 to PO43- species in line with an improvement of the adsorption performance of CrNiFe-MOF when the pH increases, i.e., when HPO42- and PO43- become more predominant. These calculations also supported that the incorporation of Cr metal sites in the oxo-trimer is expected to boost the phosphate affinity of the MOF. Finally, our work provides an easy and eco-friendly approach for MOF designing to enhance phosphate removal from water.

Characterization of Magnetic Biochar Modified Using the One-Step and Electrochemical Methods and Its Impact on Phosphate Adsorption

The properties and phosphate adsorption capability of the one-step method and electrochemical method in modifying peanut shell biochar have been determined. The one-step method deposits MgO and Fe3O4 onto biochar through chemical impregnation and regularly affects the functional groups and magnetic separation of biochar, thereby enhancing its ability to adsorb phosphate. In contrast, the electrochemical method is not favorable for modifying functional groups of biochar but can promote phosphate adsorption because of the formation of MgFe2O4 and Fe3O4 using electrolysis. The adsorption isotherm and kinetics data suggest that adsorption is monolayer onto a homogeneous surface and phosphate adsorption could be controlled by chemical processes. Biochar with the addition of both Fe2+ and Mg2+ shows better phosphate adsorption capability than those with barely any Fe2+ additions. It was concluded that the one-step method is a better modification method than the electrochemical method for enhancing the phosphate adsorption capability of biochars.

Efficient Adsorption Removal of Phosphate from Rural Domestic Sewage by Waste Eggshell-Modified Peanut Shell Biochar Adsorbent Materials

In order to promote the improvement of the rural living environment, the treatment of rural domestic sewage has attracted much attention in China. Meanwhile, the rural regions' sewage discharge standards are becoming increasingly stringent. However, the standard compliance rate of total phosphorus (TP) is very low, and TP has become the main limiting pollutant for the water pollutants discharge standards of rural domestic sewage treatment facilities. In this study, waste eggshell (E) was employed as a calcium source, and waste peanut shell (C) was employed as a carbon source to prepare calcium-modified biochar adsorbent materials (E-C). The resulting E-C adsorbent materials demonstrated efficient phosphate (P) adsorption from aqueous solutions over the initial pH range of 6-9 and had adsorption selectivity. At an eggshell and peanut shell mass ratio of 1:1 and a pyrolysis temperature of 800 °C, the experimental maximum adsorption capacity was 191.1 mg/g. The pseudo second-order model and Langmuir model were best at describing the adsorption process. The dominant sorption mechanism for P is that Ca(OH)2 is loaded on biochar with P to form Ca5(PO4)3OH precipitate. E-C was found to be very effective for the treatment of rural domestic sewage. The removal rate of TP in rural domestic sewage was 91-95.9%. After adsorption treatment, the discharge of TP in rural sewage met the second-grade (TP < 3 mg/L) and even first-grade (TP < 2 mg/L). This study provides an experimental basis for efficient P removal by E-C adsorbent materials and suggests possible applications in rural domestic sewage.

Application of Box-Behnken Design to Optimize Phosphate Adsorption Conditions from Water onto Novel Adsorbent CS-ZL/ZrO/Fe3O4: Characterization, Equilibrium, Isotherm, Kinetic, and Desorption Studies

Phosphate (PO₄^3-) is an essential nutrient in agriculture; however, it is hazardous to the environment if discharged in excess as in wastewater discharge and runoff from agriculture. Moreover, the stability of chitosan under acidic conditions remains a concern. To address these problems, CS-ZL/ZrO/Fe₃O₄ was synthesized using a crosslinking method as a novel adsorbent for the removal of phosphate (PO₄^3-) from water and to increase the stability of chitosan. The response surface methodology (RSM) with a Box-Behnken design (BBD)-based analysis of variance (ANOVA) was implemented. The ANOVA results clearly showed that the adsorption of PO₄^3- onto CS-ZL/ZrO/Fe₃O₄ was significant (p ≤ 0.05), with good mechanical stability. pH, dosage, and time were the three most important factors for the removal of PO₄^3-. Freundlich isotherm and pseudo-second-order kinetic models generated the best equivalents for PO₄^3- adsorption. The presence of coexisting ions for PO₄^3- removal was also studied. The results indicated no significant effect on PO₄^3- removal (p ≤ 0.05). After adsorption, PO₄^3- was easily released by 1 M NaOH, reaching 95.77% and exhibiting a good capability over three cycles. Thus, this concept is effective for increasing the stability of chitosan and is an alternative adsorbent for the removal of PO₄^3- from water.

Preparation and Coagulation Performance of Polyaluminum Lanthanum Silicate Coagulant

In order to address the growing problem of water pollution caused by the excessive discharge of contaminants and provide a better aquatic ecosystem for the public, increasing attention has been paid to the harmlessness and efficiency of coagulation. In this study, polyaluminum lanthanum silicate (PALS) was synthesized through co-polymerization as a novel coagulant to treat wastewater. FTIR, XRD, and SEM were used to analyze the morphology and structure of the material, which further confirmed that the PALS was successfully synthesized. The results indicated that PALS had a great performance in the treatment of a kaolin-humic acid suspension under the optimal synthesis conditions with Al/Si = 3, La/Si = 0.1, and basicity = 0.7. Compared with conventional coagulants, PALS exhibited a better performance at a low coagulant dose and could achieve a good removal effect for an ultraviolet wavelength less than 254 nm (UV254) (83.87%), residual turbidity (0.49 NTU), and dissolved organic carbon (DOC) (69.57%) at the optimal conditions. Additionally, the PALS showed a better effect on phosphate removal than other coagulants did, where the removal efficiency could reach 99.60%. Charge neutralization and adsorption bridging were the potential wastewater treatment mechanisms employed by the PALS, which showed varied contributions under different pH levels. The results indicated that PALS can be a promising coagulant in water treatment.

Controllable Preparation of Superparamagnetic Fe3O4@La(OH)3 Inorganic Polymer for Rapid Adsorption and Separation of Phosphate

Superparamagnetic Fe3O4 particles have been synthesized by solvothermal method, and a layer of dense silica sol polymer is coated on the surface prepared by sol-gel technique; then La(OH)3 covered the surface of silica sol polymer in an irregular shape by controlled in situ growth technology. These magnetic materials are characterized by TEM, FT-IR, XRD, SEM, EDS and VSM; the results show that La(OH)3 nanoparticles have successfully modified on Fe3O4 surface. The prepared Fe3O4@La(OH)3 inorganic polymer has been used as adsorbent to remove phosphate efficiently. The effects of solution pH, adsorbent dosage and co-existing ions on phosphate removal are investigated. Moreover, the adsorption kinetic equation and isothermal model are used to describe the adsorption performance of Fe3O4@La(OH)3. It was observed that Fe3O4@La(OH)3 exhibits a fast equilibrium time of 20 min, high phosphate removal rate (>95.7%), high sorption capacity of 63.72 mgP/g, excellent selectivity for phosphate in the presence of competing ions, under the conditions of phosphate concentration 30 mgP/L, pH = 7, adsorbent dose 0.6 g/L and room temperature. The phosphate adsorption process by Fe3O4@La(OH)3 is best described by the pseudo-second-order equation and Langmuir isotherm model. Furthermore, the real samples and reusability experiment indicate that Fe3O4@La(OH)3 could be regenerated after desorption, and 92.78% phosphate removing remained after five cycles. Therefore, La(OH)3 nanoparticles deposited on the surface of monodisperse Fe3O4 microspheres have been synthesized for the first time by a controlled in-situ growth method. Experiments have proved that Fe3O4@La(OH)3 particles with fast separability, large adsorption capacity and easy reusability can be used as a promising material in the treatment of phosphate wastewater or organic pollutants containing phosphoric acid functional group.

Two-Dimensional Modeling of Nano Zero-Valent Iron Transport and Retention before and after Phosphate Adsorption

The mobility of nano zero-valent iron (nZVI) will greatly affect its practical application as a remediation material for contaminated groundwater. One-dimensional (1D) column tests are commonly used in previous work to study its migration behavior, but the two-dimensional (2D) test is still very limited. This study reports a novel research system to study the 2D transport and retention behavior of colloids and solutes, which includes a 2D model test setup and the corresponding image analysis method. The transport behaviors of methyl orange (MO), nZVI, and phosphate-loaded nZVI (PnZVI) are studied using this system. The results show that the research system can reasonably describe the tempo-spatial concentration distribution of colloids and solutes. After phosphate adsorption, the mobility of nZVI is enhanced due to the increase in negative surface charge, which implies a potential environmental risk of nZVI to facilitate contaminant transport. The migration of PnZVI is not significantly influenced by its density, which is faster than MO in the longitudinal direction. The range of the plume of PnZVI in the longitudinal direction is larger than that of MO, which implies that PnZVI has a stronger longitudinal dispersion than MO.

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.

Remazol Brilliant Blue R (RBBR) dye and phosphate adsorption by calcium alginate beads modified with polyethyleneimine

This study concerns the preparation of novel adsorbent prepared from calcium alginate bead modified with polyethyleneimine (PEI-CaAlg). The adsorption capacity of the PEI-CaAlg was examined by Remazol Brilliant Blue R (RBBR) and phosphate adsorption. PEI-CaAlg showed high removal efficiencies for RBBR (90.48%) and phosphate (88.10%). The removal of both RBBR and phosphate onto the PEI-CaAlg followed the Freundlich isotherm and the second-order model. The adsorption was studied in terms of thermodynamic and found to be feasible and spontaneous in nature. The reusability of the modified alginate beads was also examined up to five cycles. The removal efficiency was 90.48% at the first cycle and decreased to 75.15% at the end of the fourth cycle. The adsorption of color and phosphate from real textile wastewater was also instigated. The removal efficiencies for color and phosphate ions reached 80.24% and 90.00%, respectively. Therefore, the prepared PEI-CaAlg can be considered as a novel, eco-friendly, and cost-effective adsorbent for simultaneous dye and phosphate adsorption. PRACTITIONER POINTS: This study aims to modify the surface of calcium alginate beads with polyethyleneimine (PEI). The adsorption of RBBR and phosphate by the modified alginate beads (PEI-CaAlg) was investigated. PEI is an organic polymer with a linear/branch shape, which can increase the active sites on the adsorbent surface. PEI has one nitrogen atom in every three atoms provides a positive charge that can complex with the negatively charged molecules. The adsorption of RBBR and phosphate were carried out onto PEI-CaAlg.

Efficient and additive-free synthesis of morphology variant iron oxyhydroxide nanostructures for phosphate adsorption application

Iron oxyhydroxide (FeOOH) nanostructures of different shapes were successfully synthesized on flexible textile cloth of polyester using a novel and simple technique based on hydrolysis method. The technique used herein is newly designed specifically to improve the efficiency in terms of energy, simplicity and cost involved in large scale synthesis of nanostructured thin films. Additionally, the morphology of nano-sized iron oxyhydroxide could be tuned into different shapes through variation in the type of precursors used for synthesis. The uniformity and adhesion of the depositions were also found to be excellent as examined by qualitative techniques. The as-deposited samples exhibited monoclinic and orthorhombic structures of FeOOH. A significant variation in the shape of as-deposited FeOOH nanostructures with change in precursor was observed through morphological studies, which displayed lance-shaped, rounded clusters and rod-like growth features in different cases. The nanocrystalline FeOOH can be directly applied to attract and trap phosphate from water reservoirs, thus contributing to environmental solutions. The proposed technique can also be utilized to deposit larger areas, which could be suitable for practical applications.

Confined La2O3 particles in mesoporous carbon material for enhanced phosphate adsorption

Novel phosphate adsorbents with confined La2O3 inside mesoporous carbon were fabricated by the solid-state grinding method using pristine mesoporous carbon material CMK-3 (PCMK-3) and oxidized CMK-3 (OCMK-3) as the matrixes (denoted as La2O3@PCMK-3 and La2O3@OCMK-3). Compared with pure La2O3, La2O3@PCMK-3 and La2O3@OCMK-3 exhibited higher normalized phosphate adsorption capacity, indicative of efficient loading of La2O3 inside the mesopores of the carbon materials. Furthermore, La2O3 loading led to substantially enhanced phosphate adsorption. The adsorption capacities of La2O3@OCMK-3 samples were higher than those of La2O3@PCMK-3 samples, possibly owing to the oxygen-containing groups forming in OCMK-3 during HNO3 oxidation, which enhanced the dispersion of La2O3 in the mesopores of OCMK-3. The adsorption capacities of La2O3@PCMK-3 and La2O3@OCMK-3 increased with the La2O3 loading amount. Phosphate adsorption onto La2O3(14.7)@PCMK-3 followed the pseudo-second-order kinetics with respect to correlation coefficient values (larger than 0.99). As pH increased from 3.4 to 12.0, the phosphate adsorption amounts of La2O3(14.7)@PCMK-3 and La2O3(15.7)@OCMK-3 decreased from 37.64 mg g-1 and 37.08 mg g-1 to 21.92 mg g-1 and 14.18 mg g-1, respectively. Additionally, La2O3@PCMK-3 showed higher adsorption selectivity towards phosphate than coexisting Cl-,NO 3 - andSO 4 2 - . The adsorbent La2O3(14.7)@PCMK-3 remained stable after five regeneration cycles.

Radiation Synthesis of Pentaethylene Hexamine Functionalized Cotton Linter for Effective Removal of Phosphate: Batch and Dynamic Flow Mode Studies

A quaternized cotton linter fiber (QCLF) based adsorbent for removal of phosphate was prepared by grafting glycidyl methacrylate onto cotton linter and subsequent ring-opening reaction of epoxy groups and further quaternization. The adsorption behavior of the QCLF for phosphate was evaluated in a batch and column experiment. The batch experiment demonstrated that the adsorption process followed pseudo-second-order kinetics with an R² value of 0.9967, and the Langmuir model with R² value of 0.9952. The theoretical maximum adsorption capacity reached 152.44 mg/g. The experimental data of the fixed-bed column were well fitted with the Thomas and Yoon-Nelson models, and the adsorption capacity of phosphate at 100 mg/L and flow rate 1 mL/min reached 141.58 mg/g. The saturated QCLF could be regenerated by eluting with 1 M HCl.

Effective adsorption of phosphate from wastewaters by big composite pellets made of reduced steel slag and iron ore concentrate

In order to remove phosphate from wastewater, a large plastic adsorption column filled with big phosphate-adsorbing pellets with diameters of 10 mm, heated by electromagnetic induction coils, was conceived. It was found that the prepared big pellets, which were made of reduced steel slag and iron ore concentrate, contain magnetic Fe and Fe3O4. The thermodynamics and kinetics of adsorption of phosphate from synthetic wastewaters on the pellets were studied in this work. The phosphate adsorption on the pellets followed three models of Freundlich, Langmuir and Dubinin-Kaganer-Radushkevick. The maximum phosphate adsorption capacity Qmax of the pellets were 2.46, 2.74 and 2.77 mg/g for the three temperatures of 20°C, 30°C and 40°C, respectively, based on the Langmuir model. The apparent adsorption energies were -12.9 kJ/mol for the three temperatures. It implied that ion exchange was the main mechanism involved in the adsorption processes. The adsorbed phosphate existed on the pellet surface mainly in the form of Fe3(PO4)2. A reduction pre-treatment of the pellet precursor with H2 greatly enhanced pellet adsorption for phosphate. The adsorption kinetics is better represented by a pseudo-first-order model. The adsorbed phosphate amounts were similar for both real and synthetic wastewaters under similar adsorption conditions. The percentage of adsorbed phosphate for a real wastewater increased with increasing pellet concentration and reached 99.2% at a pellet concentration of 64 (g/L). Some specific phosphate adsorption mechanisms for the pellets were revealed and the pellets showed the potential to efficiently adsorb phosphate from a huge amount of real wastewaters in an industrial scale.