Fabrication of porous adsorbent by quinoa husk stabilized foam templates for dye adsorption and carbonization for soil remediation.

In this study, a novel adsorbent with a sufficient porous structure was fabricated using a green and highly stable water-based foam template. This template was stabilized with agricultural waste quinoa husk (QH) and applied to remove dye pollutants in wastewater. The porous adsorbent exhibited a high adsorption capacity of 740.95 mg/g for methylene blue and 1022.1 mg/g for methyl violet. The adsorption process was well described by the Langmuir-Freundlich model and the pseudo second-order kinetic model. A sustainable concept for handling the spent adsorbent was also proposed, involving its conversion into biochar and safe return to the soil. An additional benefit was observed, as the biochar effectively adjusted the physicochemical properties of the soil and improved crop growth with the addition of 1 wt%. The potential application of porous adsorbent in wastewater treatment and the reference of sustainable strategy for disposing of other adsorbents are both noteworthy.

Simultaneous degradation of binary fluoroquinolone antibiotics by B and N in-situ self-doped guar gum hydrogel.

Using guar gum (GG) as the raw material and borax (B) as the cross-linker, zeolitic imidazolate framework-8 (ZIF-8) was in-situ loaded into the 3D network of GG hydrogel, forming a highly efficient catalytic material GG-B-ZIF-8 combined with a subsequent low-temperature calcination process. In GG-B-ZIF-8 activated peroxymonosulfate (PMS) system, binary norfloxacin (NOR) and ciprofloxacin (CIP) could be removed simultaneously, with the degradation efficiency of >99.9% within 1 h. This system was adaptable to a wide pH range of 3.0-9.0, and was also highly resistant to 5-20 mM Cl- and 10-40 mg/L humic acid. The degradation process was dominated by free radical O2•-, non-radical 1O2 and electron transfer, with eleven degradation products identified for NOR and nine for CIP via eight possible degradation pathways. Finally, the potential eco-toxicity of NOR, CIP and degradation intermediates was evaluated using the ECOSAR method.

Spectral Classification of Large-Scale Blended (Micro)Plastics Using FT-IR Raw Spectra and Image-Based Machine Learning.

Microplastics (MPs) are currently recognized as emerging pollutants; their identification and classification are therefore essential during their monitoring and management. In contrast to most studies based on small datasets and library searches, this study developed and compared four machine learning-based classifiers and two large-scale blended plastic datasets, where a 1D convolutional neural network (CNN), decision tree, and random forest (RF) were fed with raw spectral data from Fourier transform infrared spectroscopy, while a 2D CNN used the corresponding spectral images as the input. With an overall accuracy of 96.43% on a small dataset and 97.44% on a large dataset, the 1D CNN outperformed other models. The 1D CNN was the best at predicting environment samples, while the RF was the most robust with less spectral data. Overall, RF and 2D CNNs might be evaluated for plastic identification with fewer spectral data; however, 1D CNNs were thought to be the most effective with sufficient spectral data. Accordingly, an open-source MP spectroscopic analysis tool was developed to facilitate a quick and accurate analysis of existing MP samples.

[Water Quality Assessment and Spatial-temporal Variation Analysis in Yellow River Basin].

During the implementation of ecological protection in the Yellow River basin, understanding the water pollution status and spatio-temporal variation of water quality has become the most important thing for water safety in the basin. To analyze the water quality in recent years, the water quality data in the Yellow River basin from 2004 to 2018 were firstly collected from eight typical monitoring stations. Using a combination of multivariate data analysis methods including the Mann-Kendall (M-K) trend test, hierarchical clustering analysis (HCA), principal component analysis (PCA), and modified comprehensive water quality identification index (WQI), the spatio-temporal variation characteristics of the water quality were then explored in the Yellow River basin. The results indicated that in terms of time variation, the HCA from the water quality time series showed that the water quality of the Yellow River basin could be divided into the wet season, normal season, and dry season, being basically consistent with the hydrological period. Combined with the M-K trend test and WQI-based water quality assessment, the water quality of the Yellow River basin was improving gradually, with 2010 as the critical year. The water quality in the wet season was superior to that in the dry season. The pollution indicator NH4+-N and permanganate index were dominant in both the wet season and dry season. According to the spatial variation analysis, the water quality for all the studied stations improved significantly. Spatial clustering showed that the S6 (Shanxi Yuncheng Hejin Bridge) was obviously different from others, and further comparative study demonstrated that S6 was constantly seriously polluted. The S7 (Henan Jiyuan Xiaolangdi) exhibited different characteristics in the wet and dry season. In all stations, NH4+-N was considered to be the most common pollution indicator, whereas the permanganate index and DO were also relatively serious for S6. In different hydrological seasons, NH4+-N and the permanganate index showed different characteristics, and their variety was related to the fact that the former mainly came from domestic and industrial sources, whereas the latter was mainly derived from agricultural sources. The modified WQI showed obvious advantages over single-factor water quality assessment, and the findings from this study can provide scientific evidence for water pollution control and comprehensive water quality management in the Yellow River basin.

Lattice B-doping evolved ferromagnetic perovskite-like catalyst for enhancing persulfate-based degradation of norfloxacin.

Series of B-doped perovskite-like materials CeCu0.5Co0.5O3 (B-C3O) were fabricated with unique ferromagnetic property due to partial substitution of non-magnetic 2p-impurities boron in the lattice. Then, B-C3O was used for activating peroxymonosulfate (PMS) for the degradation of norfloxacin (NOR), one kind of emerging pollutants with the concentration level up to mg/L in wastewaters. The results indicated that 5.0% B-C3O exhibited stable catalytic ability at pH 3.0-9.0 and high degradation efficiency in co-existing inorganic Cl-, SO42-, NO3-, H2PO4- and organic humic acid. Non-radical 1O2, radicals •OH and SO4•-, as well as ClO- were detected with synergy effect for NOR degradation. By quantifying free radicals, •OH with 0.52 µM and SO4•- with 10.91 µM were obtained at 180 min, verifying the leading role of SO4•-. The degradation process involved the defluorination and decarboxylation, as well as opening of quinolone and piperazinyl rings. Adopting alfalfa as the model plant, the toxicity effect before and after NOR degradation was finally evaluated with seed germination rate and chlorophyll content as the physiological indicators. In summary, non-metal B-doping not only provides a creative strategy for the development of ferromagnetic perovskite-like materials, but also affords excellent catalysts for aiding the advanced oxidation technology for removal of emerging pollutants in wastewaters.

Preparation and oil absorbency of kapok-g-butyl methacrylate.

Butyl methacrylate (BMA) was grafted onto kapok fiber using benzoyl peroxide (BPO) as initiator. The structure of the grafted kapok was investigated using Fourier transform infrared spectroscopy and scanning electron microscopy. The results illustrated that BMA was successfully grafted onto the kapok fiber surface. The effects of monomer concentration, temperature and time on the oil absorbency of grafted kapok fiber were investigated. The oil absorbencies of raw kapok, NaClO2-treated kapok fiber and kapok-g-butyl methacrylate were evaluated and compared. Compared with raw kapok fiber, grafted kapok fiber showed the highest oil absorbency, with the increase percentage of 63.4%, 42.5% and 56.4% for chloroform, toluene and n-hexane, respectively. Furthermore, the as-developed grafted kapok fiber exhibited excellent reusability, and can be utilized as an eco-friendly material for recovering oil released into the surroundings.

Natural cellulose fiber derived hollow-tubular-oriented polydopamine: In-situ formation of Ag nanoparticles for reduction of 4-nitrophenol.

A facile method was reported to achieve hollow-tubular-oriented polydopamine (HTO-PDA) layer using natural kapok fiber (KF) as the bio-template without any pretreatments by altering hydrophobic fiber into hydrophilic one. Subsequently, the HTO-PDA can be utilized for direct in-situ deposition of Ag nanoparticles (NPs). The structures of pristine fiber and HTO-PDA, as well as the resulting Ag NPs attached HTO-PDA (Ag@HTO-PDA) were well characterized by means of scanning electron microscopy (SEM) coupled energy dispersion spectrum (EDS), x-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. Due to the presence of relatively uniform Ag NPs attached onto PDA layer, Ag@KF-HTO-PDA shows stable catalytic ability towards the reduction of 4-nitrophenol into its amino derivative. Further, this method was used for facile fabrication of Calotropis gigantea fiber derived, surface-functionalized material. The experimental data demonstrated also its excellent catalytic efficiency towards 4-nitrophenol reduction.

Oriented growth of poly(m-phenylenediamine) on Calotropis gigantea fiber for rapid adsorption of ciprofloxacin.

A facile polymerization of m-phenylenediamine (mPD) in methanol/water (50:50, v/v) was performed via conventional chemical oxidative method by using Calotropis gigantea fiber (CGF) as the natural biotemplate. The as-prepared CGF oriented poly(m-phenylenediamine) (PmPD), i.e. CGF-O-PmPD, exhibits a well defined fiber-oriented morphology. The presence of PmPD layer enables CGF-O-PmPD to present roughen surface with N-rich functional groups that can show high performance for the adsorption of ciprofloxacin. The variables affecting the adsorption capacity were systematically investigated, including contact time, initial concentration, initial pH, ion strength, and so forth. The experimental data reveal that with increasing the amount of mPD from 0.2, 0.5 to 2.0 g, the adsorption capacity for ciprofloxacin shows a monotonic decrease, while the adsorption kinetics show a monotonic increase, with the adsorption percentage from >50%, >60% to >70% within 10 s, demonstrating its superfast adsorption kinetics for ciprofloxacin. In addition, an increasing adsorption capacity is observed over the pH range studied, with the adsorption capacity from 0.73 to 6.7 mg g-1 at pH 2.0 to 64.9-77.3 mg g-1 at pH 10.0. After five adsorption-desorption cycles, the adsorption capacity of CGF-O-PmPD for ciprofloxacin shows no significant decrease, indicating its excellent reusability and potential application in treating antibiotic-containing wastewater.

Fabrication of magnetic macroporous chitosan-g-poly (acrylic acid) hydrogel for removal of Cd2+ and Pb2.

A novel macroporous magnetic macroporous chitosan-g-poly (acrylic acid) hydrogel adsorbent was fabricated from the Pickering high internal emulsions template stabilized by modified Fe3O4 nanoparticles. The structure and composition of modified Fe3O4 and macroporous magnetic hydrogel were characterized by TEM, XRD, TG and SEM techniques. The characterization results suggest that the Fe3O4 nanoparticles have been modified successfully with organosilane of 3-aminopropyltrimethoxysilane (APTES), and the porous structure of the macroporous hydrogel can be tuned with the amount of stabilized particles, volume fraction of dispersed phase and the amount of the cosurfactant. Adsorption experiments indicate that the adsorption equilibrium was rapidly reached within 20min and the maximal adsorption capacities were determined to be 308.84mg/g for Cd2+ and 695.22mg/g for Pb2+. After five adsorption-desorption cycles, the adsorbent can retain its high adsorption capacity. The introduction of Fe3O4 is beneficial to the recycle of adsorbent after usage.

Fabrication of magnetic hydroxypropyl cellulose-g-poly(acrylic acid) porous spheres via Pickering high internal phase emulsion for removal of Cu(2+) and Cd(2.).

A series of magnetic hydroxypropyl cellulose-g-poly(acrylic acid) porous spheres were prepared via O/W Pickering high internal phase emulsions (HIPEs) integrated precipitation polymerization. The structure and composition of modified Fe3O4 and porous structures were characterized by TEM, XRD, TGA and SEM. The results indicated that the silanized Fe3O4 can influence greatly the pore structure of magnetic porous sphere in addition to non-negligible impacts of the proportion of mixed solvent and co-surfactant. The adsorption experiment demonstrated that the adsorption equilibrium can be reached within 40min and the maximal adsorption capacity was 300.00mg/g for Cd(2+) and 242.72mg/g for Cu(2+), suggesting its fast adsorption kinetics and high adsorption capacity. After five adsorption-desorption cycles, no significant changes in the adsorption capacity were observed, suggesting its excellent reusability. The magnetic porous sphere can be easily separated from the solution and then find its potential as a recyclable material for highly efficient removal of heavy metals.

Rapid enrichment of rare-earth metals by carboxymethyl cellulose-based open-cellular hydrogel adsorbent from HIPEs template.

A series of monolithic open-cellular hydrogel adsorbents based on carboxymethylcellulose (CMC) were prepared through high internal phase emulsions (HIPEs) and used to enrich the rare-earth metals La(3+) and Ce(3+). The changes of pore structure, and the effects of pH, contact time, initial concentration on the adsorption performance were systematically studied. The results show that the as-prepared monolithic hydrogel adsorbents possess good open-cellular framework structure and have fast adsorption kinetics and high adsorption capacity for La(3+) and Ce(3+). The involved adsorption system can reach equilibrium within 30min and the maximal adsorption capacity is determined to be 384.62mg/g for La(3+) and 333.33mg/g for Ce(3+). Moreover, these porous hydrogel adsorbents show an excellent adsorptive reusability for La(3+) and Ce(3+) through five adsorption-desorption cycles. Such a pore hierarchy structure makes this monolithic open-cellular hydrogel adsorbent be an effective adsorbent for effective enrichment of La(3+) and Ce(3+) from aqueous solution.

Research and application of kapok fiber as an absorbing material: a mini review.

Kapok fiber corresponds to the seed hairs of the kapok tree (Ceiba pentandra), and is a typical cellulosic fiber with the features of thin cell wall, large lumen, low density and hydrophobic-oleophilic properties. As a type of renewable natural plant fiber, kapok fiber is abundant, biocompatible and biodegradable, and its full exploration and potential application have received increasing attention in both academic and industrial fields. Based on the structure and properties of kapok fiber, this review provides a summary of recent research on kapok fiber including chemical and physical treatments, kapok fiber-based composite materials, and the application of kapok fiber as an absorbent material for oils, metal ions, dyes, and sound, with special attention to its use as an oil-absorbing material, one predominant application of kapok fiber in the coming future.

In situ generation of silver nanoparticles within crosslinked 3D guar gum networks for catalytic reduction.

The direct use of guar gum (GG) as a green reducing agent for the facile production of highly stable silver nanoparticles (Ag NPs) within this biopolymer and subsequent crosslinking with borax to form crosslinked Ag@GG beads with a 3D-structured network are presented here. These crosslinked Ag@GG beads were characterized using UV-vis absorption spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy, and then tested as a solid-phase heterogenerous catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of excess borohydride. The results indicate that these crosslinked Ag@GG beads show excellent catalytic performance for the reduction of 4-NP within 20 min and can be readily used for 10 successive cycles.

A simple approach to fabricate granular adsorbent for adsorption of rare elements.

A kind of granular hybrid hydrogel was prepared under an ambient temperature in air atmosphere using Fenton reagent as the redox initiator, and its three-dimensional structured polymeric network can be formed by the grafting reaction of acrylic acid (AA) onto hydroxypropyl cellulose (HPC) with attapulgite (APT) as the inorganic component. The resulting granular hybrid hydrogel was marked as HPC-g-PAA/APT and used as the adsorbent to remove the rare earth elements, La(III) and Ce(III). The effects of pH and APT content on the adsorption capacity, as well as the adsorption isotherms and kinetics, were systematically investigated. Finally, the reusability of HPC-g-PAA/APT for La(III) and Ce(III) were evaluated. The results indicate that the adsorption process is pH-independent at pH ≥ 4.0 and can be described using the pseudo-second-order kinetic model. The equilibrium isotherm matches well with the Langmuir model. The adsorbed La(III) and Ce(III) can be desorbed by 0.5 mol/L HCl, with the desorption percentage of 80% for La(III) and Ce(III). After five adsorption-desorption cycles, the adsorption capacity shows a slight decrease (about 15%), implying that the granular hybrid hydrogel can be used as an effective adsorbent for the removal and recovery of La(III) and Ce(III) from aqueous solution.

Kinetic and thermodynamic studies on the removal of oil from water using superhydrophobic kapok fiber.

In this paper, an oil sorbent based on superhydrophobic kapok fiber fabricated by the sol-gel method was used for the selective sorption of oil from the surface of artificial seawater. The effects of process parameters such as seawater pH, seawater temperature, and contact time on the extent of oil sorption were investigated. The as-prepared fiber showed higher oil sorption capacity than raw fiber in both the trenchant acid and alkaline seawater environment. Results of the kinetic studies show that the sorption process follows pseudo-second-order reaction kinetics. The thermodynamic investigations demonstrate that the sorption process is spontaneous and endothermic. In addition, the as-prepared fiber can float on the water surface after the sorption of oil, which facilitates the post-processing of oil-loaded fiber. The modified fiber might provide a simple method for the removal and collection of oil on the water surface.

Investigation of acetylated kapok fibers on the sorption of oil in water.

Kapok fibers have been acetylated for oil spill cleanup in the aqueous environment. The structures of raw and acetylated kapok fiber were characterized using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). Without severe damage to the lumen structures, the kapok fibers were successfully acetylated and the resulting fibers exhibited a better oil sorption capacity than raw fibers for diesel and soybean oil. Compared with high viscosity soybean oil, low viscosity diesel shows a better affinity to the surface of acetylated fibers. Sorption kinetics is fitted well by the pseudo second-order model, and the equilibrium data can be described by the Freundlich isotherm model. The results implied that acetylated kapok fiber can be used as the substitute for non-biodegradable oil sorption materials.

Coated kapok fiber for removal of spilled oil.

Based on raw kapok fiber, two kinds of oil absorbers with high sorption capacity were prepared by a facile solution-immersion process. The coated polymer with low surface energy and rough fiber surface play important role in the retention of oil. The as-prepared fiber can quickly absorb gasoline, diesel, soybean oil, and paraffin oil up to above 74.5%, 66.8%, 64.4% and 47.8% of oil sorption capacity of raw fiber, respectively. The absorbed oils can be easily recovered by a simple vacuum filtration and the recovered coated-fiber still can be used for several cycles without obvious loss in oil sorption capacity. The thermodynamic study indicates that the adsorption process is spontaneous and exothermic, with complex physisorption and chemisorption. The results suggest that the coated fiber can be used as a low-cost alternative for the removal of oil spilled on water surface.

Chitosan-g-poly(acrylic acid) hydrogel with crosslinked polymeric networks for Ni2+ recovery.

In this study, chitosan-g-poly(acrylic acid) (CTS-g-PAA) hydrogel with crosslinked polymeric networks was prepared from an aqueous dispersion polymerization and then used as the adsorbent to recover a valuable metal, Ni2+. The adsorption capacity of CTS-g-PAA for Ni2+ was evaluated and the adsorption kinetics was investigated using Voigt-based model and pseudo-second-order model. In addition, the effects of pH values and coexisting heavy metal ions such as Cu2+ and Pb2+ on the adsorption capacity were studied. The results indicate that the as-prepared adsorbent has faster adsorption rate and higher adsorption capacity for Ni2+ recovery, with the maximum adsorption capacity of 161.80 mg g(-1). In a wide pH range of 3-7, the adsorption capacity keeps almost the same, and even under competitive conditions, the adsorption capacity of CTS-g-PAA for Ni2+ is observed to be as high as 54.47 mg g(-1). Finally, the adsorption performance of CTS-g-PAA for Ni2+ in real water sample and the reusability of the as-prepared adsorbent were evaluated, and also the controlled adsorption mechanism was proposed.

Enhanced adsorption of Methylene Blue from aqueous solution by chitosan-g-poly (acrylic acid)/vermiculite hydrogel composites.

A series of chitosan-g-poly (acrylic acid)/vermiculite hydrogel composites were synthesized and used as adsorbents for the investigation of the effect of process parameters such as vermiculite content, pH of dye solution, contact time, initial concentration of dye solution, temperature, ionic strength and concentration of surfactant sodium dodecyl sulfate on the removal of Methylene Blue (MB) from aqueous solution. The results showed that the adsorption capacity for dye increased with increasing pH, contact time and initial dye concentration, but decreased with increasing temperature, ionic strength and sodium dodecyl sulfate concentration in the present of the surfactant. The adsorption kinetics of MB onto the hydrogel composite followed pseudo second-order kinetics and the adsorption equilibrium data obeyed Langmuir isotherm. By introducing 10 wt.% vermiculite into chitosan-g-poly (acrylic acid) polymeric network, the obtaining hydrogel composite showed the highest adsorption capacity for MB, and then could be regarded as a potential adsorbent for cationic dye removal in a wastewater treatment process.

[Adsorption of Pb2+ onto chitosan-grafted-poly (acrylic acid )/sepiolite composite].

A composite adsorbent chitosan-grafted-poly(acrylic acid)/sepiolite was prepared, and its pH-dependence for removing Pb2+, as well as adsorption isotherm and kinetics were estimated. The results indicate that poly (acrylic acid) has been grafted onto the backbone of chitosan, forming an organic-inorganic composite adsorbent. As-prepared adsorbent shows a coarse, porous and accidented surface, which can contribute to its adsorption kinetics. Under the conditions of pH 6.00, contact time of 30 min, initial Pb2+ concentration of 0.02 mol x L(-1) and amount of adsorbent of 0.10 g, the adsorption capacity of developed adsorbent for Pb2+ is found to be 638.9 mg x g(-1), about three times than that of sepiolite. When five cycles of adsorption-desorption process were carried out, the adsorption capacity decreased to 489.2 mg x g(-1), 76.6% to its original adsorption capacity. However, when sepiolite was used as the adsorbent, no sorption can be observed after three cycles of adsorption-desorption process. Compared to sepiolite, this composite adsorbent presents higher adsorption capacity, faster adsorption rate and better reusable ability.