Fabrication and evaluation of a regenerable HFO-doped agricultural waste for enhanced adsorption affinity towards phosphate

Renewable cellulose aerogel embedded with nano-HFO for preferable phosphate capture from aqueous solution

Excess phosphate in water can cause eutrophication, which must be addressed. Despite many efforts devoted to the adsorptive removal of phosphate from water, the development of new adsorbents with high adsorption capacity is highly desirable. Herein, a novel nanocomposite was proposed for phosphate removal by confining hydrated ferric oxide (HFO) nanoparticles into a cellulose aerogel (CA) network named as HFO@CA. Benefiting from the characteristics of the low density and porous structure of CA, the internal surface of the nanocomposite is more accessible and thus improves the utilization of the HFO nanoparticles. Batch adsorption experiments were carried out to evaluate the phosphate uptake by the prepared adsorbent. The maximum adsorption capacity of HFO@CA occurs at near-acidic pH. With increasing temperature, the composite adsorbent is more favorable for phosphate adsorption. Moreover, the hybrid aerogel exhibited fast kinetic behavior for phosphate removal, which could be accurately depicted by pseudo-second-order model. HFO@CA shows excellent adsorption selectivity in solutions containing competitive anions at higher levels. In addition, five cycles of the phosphate adsorption experiments without obvious capacity loss indicated that HFO@CA has great regenerability. These results demonstrate that HFO@CA has a wide field of application with good prospects in phosphate removal from wastewater, which also provides a new strategy to prepare adsorbents with excellent performance using renewable cellulose resources.

Synthesis of layered double hydroxide-based hybrid electrode for efficient removal of phosphate ions in capacitive deionization

The removal of phosphate ions by capacitive deionization has become one of the most frontier research topics in the water treatment field in recent years. In this work, hybrid electrodes composed of nickel-iron layered double hydroxide (NiFe-LDH) - anchored on activated carbon fiber (ACF)-were synthesized by a hydrothermal method and subsequently applied in capacitive deionization to remove phosphate ions. The adsorption performance of the two hybrid electrodes on phosphate ions was compared by capacitive deionization experiments. The experiment was carried out for 3 hours to reach equilibrium, and the optimum adsorption of 33.48 mg/g was obtained using NiFe-LDH/ACF-2 hybrid electrode at room temperature (25 °C) and pH = 6.0. The results showed that increasing the loading capacity of NiFe-LDH on ACF might enhance the adsorption capacity of phosphate ions. Furthermore, the calculation of adsorption kinetics and adsorption isotherms elucidated that the adsorption capacity increased with the increasing of applied voltage. Meanwhile, the experimental data were fitted well with pseudo-first-order kinetics and Langmuir isotherms. Notably, it was observed that the pH first increased, then decreased during the adsorption due to the electrolysis of water, while the form of phosphate ions was transformed, with low pH favoring the adsorption of phosphate ions.

Enhanced removal of phosphate using pomegranate peel-modified nickel‑lanthanum hydroxide

In this work, a bimetallic Ni/La nanoparticle-laded biosorbent was fabricated from pomegranate fibers by solvothermal synthesis method. The material exhibited a high-efficient phosphate removal capability. The results of the characterization analysis showed that the surface of pomegranate fibers was rough and evenly coated with Ni and La after modification, and the specific surface area of Ni-La@Peel increased to 50.20 m²/g, providing a large number of adsorption sites for phosphate removal. The maximum phosphate removal rate of adsorbent was higher than 97% in a wide pH range (3.7-10.8). The maximum adsorption capacities of Ni-La@Peel were 226.55 mg-P/g and 220.31 mg-P/g under alkaline and acidic conditions, respectively, as calculated using the Langmuir model. Meanwhile, all the results were consistent with the Langmuir isothermal (R² = 0.99) and kinetic pseudo-second order models (R² = 0.99), indicating that the phosphate removal mechanism of Ni-La@Peel was mainly related to homogeneous chemisorption. Experimental results showed that in the presence of other anions, such as chloride, sulfate, nitrate, bromide and fluoride, the adsorption capacity of phosphate was only reduced by about 10% compared to the blank sample individually. In addition, the phosphate removal efficiency of Ni-La@Peel remained 82.05% at 7th adsorption-desorption cycle. These findings show that Ni-La@Peel is a promising material for purification of phosphate-containing wastewater.

Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery. Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk, a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of FeOOH/anion exchanger nanocomposites (Fe/900s) with enhanced metal site utilization and reduced metal leakage risk. Compared to composites prepared using alkaline precipitation methods, Fe/900s performed comparably, with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L, a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO₄^2-/L, and high long-term resilience (with a capacity loss of ~14% after five cycles), along with substantially lower Fe loading amount (4.11 wt.%) and Fe leakage percentage. Mechanistic investigation demonstrated that contribution of the specific FeOOH sites to phosphate adsorption increased substantially (up to 50.97% under the optimal conditions), in which Fe(III)-OH was the dominant efficient species. The side effects of an excessively long reaction time, which included quaternary ammonium decomposition, FeOOH aggregation, and Fe(III) reduction, were discussed as guidance for optimizing the synthesis strategy. The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.

Effectiveness and mechanism of aluminum/iron co-modified calcite capping and amendment for controlling phosphorus release from sediments

The effectiveness and mechanism of aluminum/iron co-modified calcite (Al/Fe-CA) for the control of phosphorus (P) liberation from sediments was investigated. The results showed that Al/Fe-CA possessed good sorption performance for phosphate, and the maximum phosphate sorption capacity for Al/Fe-CA could reach 27.0 mg/g. The major mechanisms involved the surface adsorption of phosphate on calcite, the precipitation between phosphate and Ca²⁺ leached from calcite, and the ligand exchange between Al/Fe-bound hydroxyl groups and phosphate to form the Al-O-P and Fe-O-P inner-sphere complexes. The re-releasing risk of Al/Fe-CA-bound P under the circumstances of normal pH (5-9) and reducing environment was very low. Al/Fe-CA addition could significantly reduce the risk of P releasing from sediment to overlying water (OL-water), and the inactivation of mobile P, reactive soluble P (SRP) and diffusive gradient in thin-films (DGT)-labile P in sediment by Al/Fe-CA had a great part in the suppression of sediment-P liberation to OL-water by the Al/Fe-CA amendment. Al/Fe-CA capping and fabric-wrapped Al/Fe-CA capping both could greatly reduce the risk of P releasing from sediment into OL-water, and the formation of a static layer with low concentrations of SRP and DGT-labile P in the upper sediment was the key to sustaining a high P controlling efficiency. When the applied mode of Al/Fe-CA varied from capping to amendment, although the inactivation efficiency of DGT-labile P in the overlying water and upper sediment by Al/Fe-CA would decrease to a certain degree, the inactivation efficiency of DGT-labile P in the lower sediment by Al/Fe-CA would increase. Results of this study suggest that Al/Fe-CA has the high potential to be used as an active capping or amendment material for the management of internal P loading in surface water bodies.

A novel permeable reactive biobarrier for ortho-nitrochlorobenzene pollution control in groundwater: Experimental evaluation and kinetic modelling

Three novel permeable reactive barrier (PRB) materials composed of Cu/Fe with 0.24% and 0.43% (w/w) Cu loadings or Fe⁰ supported on wheat straw were prepared (termed materials E, F and G). These materials exhibited excellent pollutant removal efficiency and physical stability as well as the ongoing release of organic carbon and iron. Column experiments showed that materials E, F and G removed almost 100% of ortho-nitrochlorobenzene (o-NCB) from water. The rates of iron release from the E and F columns exceeded those from column G but this had no significant effect on o-NCB removal. The bacteria that degraded o-NCB in E and F were also different from those in G. The levels of these bacteria in the columns were higher than those in the initial materials, with the highest level in column E. The simultaneous reduction and microbial degradation of o-NCB was observed, with the latter being dominant. A kinetic model was established to simulate the dynamic interactions and accurately predicted the experimental results. Organic carbon from the wheat straw supported the majority of the biomass in each column, which was essential for the bioremediation process. The findings of this study suggest an economically viable approach to mitigating o-NCB pollution.

Recent advances and challenges on removal and recycling of phosphate from wastewater using biomass-derived adsorbents

As the severe damage of phosphate enrichment in the water ecosystem and the supply shortage of phosphate rock, developing an efficient method for the removal and recycling of phosphate from wastewater is of great significance. To achieve this goal, adsorption technology has been widely investigated, and various adsorbents were developed. Among them, the biomass-derived adsorbents including biomass-derived carbon-based materials, biomass-based anion exchangers and metal-biomass composites have attracted increasing attention over the past years due to the low cost, abundant renewable raw materials and environmental friendliness. However, different adsorbents usually exhibit variable adsorption performances for phosphate, which highly depends on their design strategies, preparation methods and potential adsorption mechanisms. Thus, this review comprehensively summarizes the recent researches on the removal and recycling of phosphate from wastewater using the biomass-derived adsorbents. Especially, the design strategies, preparation methods, adsorption performances and mechanisms of these reported biomass-derived adsorbents are discussed in detail. Moreover, as the significant strategies to recover and recycling phosphate, the elution and direct use of phosphate-loaded adsorbents as fertilizers are also presented. Although the excellent adsorption performance has been obtained, some challenges are still existing, which should be given more attention in the following researches to facilitate the development and industrial application of biomass-derived adsorbents.

New Composite Sorbent for Removal of Sulfate Ions from Simulated and Real Groundwater in the Batch and Continuous Tests

The evaluation of groundwater quality in the Dammam formation, Faddak farm, Karbala Governorate, Iraq proved that the sulfate (SO42-) concentrations have high values; so, this water is not suitable for livestock, poultry and irrigation purposes. For reclamation of this water, manufacturing of new sorbent for permeable reactive barrier was required through precipitation of Mg and Fe hydroxides nanoparticles on the activated carbon (AC) surface with best Mg/Fe molar ratio of 7.5/2.5. Mixture of 50% coated AC and 50% scrap iron was applied to eliminate SO42- from contaminated water with efficiency of 59% and maximum capacity of adsorption equals to 9.5 mg/g for a time period of 1 h, sorbent dosage 40 g/L, and initial pH = 5 at 50 mg/L initial SO42- concentration and 200 rpm shaking speed. Characterization analyses certified that the plantation of Mg and Fe nanoparticles onto AC was achieved. Continuous tests showed that the longevity of composite sorbent is increased with thicker bed and lower influent concentration and flow rate. Computer solution (COMSOL) software was well simulated for continuous measurements. The reclamation of real contaminated groundwater was achieved in column set-up with efficiency of 70% when flow rate was 5 mL/min, bed depth was 50 cm and inlet SO42- concentration was 2301 mg/L.

Facile synthesis of Fe3O4 anchored polyaniline intercalated graphene oxide as an effective adsorbent for the removal of hexavalent chromium and phosphate ions

Adsorption media of hybrid composites is a promising candidate to eliminate the toxic contaminants from an aqueous environment, and good regeneration ability has received considerable interest to be utilized in water and wastewater treatment. Herein, we synthesized Fe₃O₄ anchored polyaniline intercalated graphene oxide (Fe₃O₄x%-PANI@GO, where x = 10, 20 and 50% of Fe₃O₄ particles) hybrid composites by co-precipitation and modified Hummers' method, followed by in-situ polymerization. The as-synthesized Fe₃O₄x%-PANI@GO acts as a potential host in welcoming the guest ions such as anionic contaminants with different interactions in this work. Besides, the advantages of easy separation by the external magnetic field, the Fe₃O₄x%-PANI@GO hybrid composite also achieve a great adsorption efficiency of 143.54 and 135.67 mg/g for Cr(VI) and phosphate ions, respectively, than the other adsorbents reported in the literature. The as-synthesized adsorbents were characterized by different analytical techniques and influencing parameters such as contact time, co-existing anions, solution pH, adsorption isotherms, and kinetics were studied in detail. The adsorption system of Fe₃O₄50%-PANI@GO hybrid composite follows the Langmuir isotherm and pseudo-second-order kinetic model for the elimination of Cr(VI) and phosphate ions from aqueous solutions. The feasible removal mechanism of Cr(VI) and phosphate ions was explored by FTIR and XPS techniques for anionic pollutants. Moreover, the selectivity and recyclability tests showed that the Fe₃O₄50%-PANI@GO hybrid composites demonstrated a high adsorption capacity towards the anionic ions from the aqueous environment. Therefore, the present investigation suggested that the Fe₃O₄50%-PANI@GO hybrid composites is an effective adsorbent for the elimination of Cr(VI) and phosphate ions from wastewater.

Solution pH affects single, sequential and binary systems of sulfamethoxazole and cadmium adsorption by self-assembled cellulose: Promotion or inhibition?

A new self-assembled cellulose (SACS) containing multi-functional amine, carboxyl and hydroxyl groups was successfully obtained through etherification, cross-linking and grafting processes. Then, the adsorption of sulfamethoxazole (SMZ) and Cd(II) onto SACS at pH values of 3, 5.7 and 7.5 was systematically investigated by batch experiments of single, sequential and binary systems, characterization and density functional theory (DFT) calculations. The presence of Cd(II) decreased the adsorption of SMZ because of hydrophilic site competition, while SMZ inversely increased the adsorption of Cd(II), which was attributed to bridging and especially to electrostatic shielding effects; moreover, both the inhibitory and synergistic effects were more obvious in the binary system and at a pH of 7.5. There was a dynamic balance between the inhibitory and synergistic effects that depended on the system, pH value and concentration ratio. DFT results further indicated that SMZ^- more easily coordinated with Cd(II) at sulfonyl oxygen and nitrogen sites, and the cationic bridge of Cd(II) with SMZ^- mainly occurred in the sequential system. Moreover, a complexation-decomplexation-complexation balance of SMZ^- and Cd(II) probably occurred in the binary system.

Mixed-culture aerobic anoxygenic photosynthetic bacterial consortia reduce nitrate: Core species dynamics, co-interactions and assessment in raw water of reservoirs

Three consortia of mixed-culture Aerobic Anoxygenic Photosynthetic Bacteria (AAPB) with excellent aerobic denitrifying ability were isolated from drinking water source reservoirs. The results showed that the removal of dissolved organic carbon (DOC) and nitrate nitrogen (NO₃^--N) by mixed-culture AAPB were higher than 90% and 99%, respectively. The Illumina MiSeq sequencing of pufM gene revealed that the dominant genera and their relative abundance changed over the culture periods. Sphingomonas sanxanigenens was the most dominant species observed at 9 h, whereas at 48 h, the most abundant species was Rhodobacter blasticus. A network analysis demonstrated that the co-interactions among the different genera were complex and variable. Mixed-culture AAPB removed more than 30% of NO₃^--N and 25% of DOC from the source water and this study suggests that mixed-culture AAPB can be regarded as a latent denitrifying microbial inoculum in the reservoir raw water treatment.

Phosphate adsorption performance and mechanisms by nanoporous biochar-iron oxides from aqueous solutions

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar-iron oxides, namely biochar-magnetite (BC-M), biochar-ferrihydrite (BC-F), biochar-goethite (BC-G), and biochar-hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar-iron oxides had huge surface areas of 691-864 m²/g and average pore diameters of 3.4-4.0 nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar-iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar-iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.

Novel Surface Modification of ZnO QDs for Paclitaxel-Targeted Drug Delivery for Lung Cancer Treatment

Adipic dihydrazide and heparin were attached to ZnO quantum dots surface, and the ZnO-adipic dihydrazide-heparin nanocomplex was used as a drug delivery system to deliver paclitaxel for chemotherapy. The surface modification and the loading of paclitaxel were confirmed by Fourier transform infrared spectrum, featured by characteristic peaks from functional groups of adipic dihydrazide, heparin, and paclitaxel. The impacts of pH on the drug release were investigated, and the cytotoxicity studies were conducted with A549 cells. The pharmacokinetic study was conducted with male Wistar rats. Both in vitro and in vivo study indicated that ZnO-adipic dihydrazide-heparin-paclitaxel nanocomplex could deliver paclitaxel in a more controllable way, and it has the potential to be a high-efficiency drug delivery system for cancer treatment.

Hussein H, H. Ragab A, S. Al-Radadi N. Synthesis and Characterization of Silica-Coated Oxyhydroxide Aluminum/Doped Polymer Nanocomposites: A Comparative Study and Its Application as a Sorbent

The present investigation is a comparison study of two nanocomposites: Nano-silica-coated oxyhydroxide aluminum (SiO2-AlOOH; SCB) and nano-silica-coated oxyhydroxide aluminum doped with polyaniline (SiO2-AlOOH-PANI; SBDP). The prepared nanocomposites were evaluated by monitoring the elimination of heavy metal Ni(II) ions from aquatic solutions. The synthesized nanocomposites were analyzed and described by applying scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) techniques, as well as Zeta potential distribution. In this study, two adsorbents were applied to investigate their adsorptive capacity to eliminate Ni(II) ions from aqueous solution. The obtained results revealed that SBDP nanocomposite has a higher negative zeta potential value (-47.2 mV) compared with SCB nanocomposite (-39.4 mV). The optimum adsorption was performed at pH 8, with approximately 94% adsorption for SCB and 97% adsorption for SBDP nanocomposites. The kinetics adsorption of Ni ions onto SCB and SBDP nanocomposites was studied by applying the pseudo first-order, pseudo second-order, and Mories-Weber models. The data revealed that the adsorption of Ni ions onto SCB and SBDP nanocomposites followed the pseudo second-order kinetic model. The equilibrium adsorption data were analyzed using three models: Langmuir, Freundlich, and Dubinin-Radusekevisch-Kanager Isotherm. It was concluded that the Langmuir isotherm fits the experimental results well for the SCB and SBDP nanocomposites. Thermodynamic data revealed that the adsorption process using SCB nanocomposites is an endothermic and spontaneous reaction. Meanwhile, the Ni ion sorption on SBDP nanocomposites is exothermic and spontaneous reaction.

Facile and Efficient Fabrication of Bandgap Tunable Carbon Quantum Dots Derived From Anthracite and Their Photoluminescence Properties

Low-cost and earth-abundant coal has been considered to have a unique structural superiority as carbon sources of carbon quantum dots (CQDs). However, it is still difficult to obtain CQDs from raw coal due to its compactibility and lower reactivity, and the majority of the current coal-based CQDs usually emit green or blue fluorescence. Herein, a facile two-step oxidation approach (K₂FeO₄ pre-oxidation and H₂O₂ oxidation) was proposed to fabricate bandgap tunable CQDs from anthracite. The K₂FeO₄ pre-oxidation can not only weaken the non-bonding forces among coal molecules which cause the expansion of coal particles, but also form a large number of active sites on the surface of coal particles. The above effects make the bandgap tunable CQDs (blue, green, or yellow fluorescence) can be quickly obtained from anthracite within 1 h in the following H₂O₂ oxidation by simply adjusting the concentration of H₂O₂. All the as-prepared CQDs contain more than 30 at% oxygen, and the average diameters of which are <10 nm. The results also indicate that the high oxygen content only can create new energy states inside the band gap of CQDs with average diameter more than 3.2 ± 0.9 nm, which make the as-prepared CQDs emit green or yellow fluorescence.