Green chemical method for the synthesis of chromogenic fiber and its application for the detection and extraction of Hg2+ and Cu2+ in environmental medium

Identification of surface-enhanced Raman spectroscopy using hybrid transformer network

Surface-enhanced Raman Spectroscopy (SERS) is extensively implemented in drug detection due to its sensitivity and non-destructive nature. Deep learning methods, which are represented by convolutional neural network (CNN), have been widely applied in identifying the spectra from SERS for powerful learning ability. However, the local receptive field of CNN limits the feature extraction of sequential spectra for suppressing the analysis results. In this study, a hybrid Transformer network, TMNet, was developed to identify SERS spectra by integrating the Transformer encoder and the multi-layer perceptron. The Transformer encoder can obtain precise feature representations of sequential spectra with the aid of self-attention, and the multi-layer perceptron efficiently transforms the representations to the final identification results. TMNet performed excellently, with identification accuracies of 99.07% for the spectra of hair containing drugs and 97.12% for those of urine containing drugs. For the spectra with additive white Gaussian, baseline background, and mixed noises, TMNet still exhibited the best performance among all the methods. Overall, the proposed method can accurately identify SERS spectra with outstanding noise resistance and excellent generalization and holds great potential for the analysis of other spectroscopy data.

Carboxyl and polyamine groups functionalized polyacrylonitrile fibers for efficient recovery of copper ions from solution

Heavy metals (e.g., Cu) in wastewater are attractive resources for diverse applications, and adsorption is a promising route to recovery of heavy metals from wastewater. However, high-performance adsorbents with high adsorption capacity, speed, and stability remain challenging. Herein, chelating fibers were prepared by chemically grafting amine and carboxyl groups onto the polyacrylonitrile fiber surface and used in the wastewater's adsorption of Cu2+. The adsorption behavior of Cu2+ on the fibers was systematically investigated, and the post-adsorption fibers were comprehensively characterized to uncover the adsorption mechanism. The results show that chelated fiber has a 136.3 mg/g maximum capacity for Cu2+ adsorption at pH = 5, and the whole adsorption process could reach equilibrium in about 60 min. The adsorption process corresponds to the quasi-secondary kinetic and Langmuir models. The results of adsorption, FTIR, and XPS tests indicate that the synergistic coordination of -COOH and -NH2 plays a leading role in the rapid capture of Cu2+. In addition, introducing hydrophilic groups facilitates the rapid contact and interaction of the fibers with Cu2+ in the solution. After being used five times, the fiber's adsorption capacity remains at over 90% of its original level.

Green synthesis of a novel functionalized chitosan adsorbent for Cu(II) adsorption from aqueous solution

Pollution generated by heavy metals has become a global environmental issue with much public concern. Herein, a functionalized chitosan-based adsorbent (CS-PAR) was synthesized via a simple one-step method for the adsorption of copper ions in solutions. A series of characterization methods have shown that CS-PAR was successfully synthesized. The experimental results showed that the maximum adsorption capacity of CS-PAR for Cu(II) ions was 170.23 mg/g. The adsorption process of Cu(II) on CS-PAR conformed to Langmuir and pseudo second-order models and belonged to a single-layer chemical adsorption process on the surface of a homogeneous medium. The adsorption mechanism of the adsorbent to Cu(II) ions was the complexation between the N-containing functional groups existing on the surface of the adsorbent and Cu(II). These results also showed that the adsorbent was an efficient material for removing heavy metal copper in wastewater and had very important practical significance.

Microwave-assisted functionalization of PAN fiber by 2-amino-5-mercapto-1,3,4-thiadiazol with high efficacy for improved and selective removal of Hg2+ from water

Mercury (Hg²⁺) contamination in water is associated with potential toxicity to human health and ecosystems. Many research studies have been ongoing to develop new materials for the remediation of Hg²⁺ pollution in water. In this study, a novel thiol- and amino-containing fibrous adsorbent was prepared by grafting 2-amino-5-mercapto-1,3,4-thiadiazol (AMTD) onto PAN fiber through a microwave-assisted method. The synthesized functional fiber was characterized by FTIR, SEM, and elemental analysis. Adsorption tests depicted that for mercury uptake, PAN_MW-AMTD fiber exhibited enhanced adsorption capacity compared with other fibrous adsorbents and selective adsorption feature under the interference of other metal ions, including Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺. The influence of pH on the adsorption process was investigated and the effect of temperature revealed that the adsorption sorption process was endothermic and the adsorption performance of PAN_MW-AMTD was elevated with the increase of temperature. Kinetic studies of PAN_MW-AMTD fiber followed the pseudo-second-order and the adsorption isotherm of Hg²⁺ was well fitted by Sips and Langmuir equations, given the maximum adsorption amount of 332.9 mg/g. XPS results suggested that a synergetic coordination effect of sulfur and nitrogen in functional fiber with mercury took responsibility for the adsorption mechanism in the uptake process. In addition, the prepared PAN_MW-AMTD fiber could easily be regenerated with 0.1 M HCl for five times without significant reduction of mercury removal efficiency. Thus, this study will facilitate the research on novel functional material for the removal of mercury from water.

Engineering of UiO-66-NH2 as selective and reusable adsorbent to enhance the removal of Au(III) from water: Kinetics, isotherm and thermodynamics

Efficient removal of gold ions from wastewater has become a hot research topic. A new metal-organic framework material (PAR-UiO-66) was prepared by post-modification of UiO-66-NH₂. A series of characterizations proved the successful preparation of PAR-UiO-66. The batch adsorption experiment was carried out. Under the room temperature (298 K) of and pH 4.0, the optimal adsorption capacity of PAR-UiO-66 for gold ions was 683.45 mg/g, which was an increase of 426.8 mg/g compared with that of UiO-66-NH₂. The adsorption of gold ions on PAR-UiO-66 accords with pseudo-second-order kinetics and Langmuir isotherm modles. The adsorption process was endothermic and spontaneous. PAR-UiO-66 has good selectivity and still has 92.5% adsorption efficiency after five repeated adsorptions. The adsorption mechanism is electrostatic attraction, reduction and chelation.

A Highly Expanded Polycarboxylate Gel and New Environmental Response Effects for Efficiently Adsorbing and Recovering Cu(II) from Water

A new highly expanded polycarboxylate gel (EPCG) was accidentally formed in a facile cross-linking copolymerization system. When used as an adsorbent material, the EPCG could be quickly expanded 29.44 times in water to have a high permeability inside for realizing the efficient adsorption toward Cu(II) from water. The adsorption capacity of EPCG toward Cu(II) was 261.70 mg/g, which was higher than that of all the selected existing adsorbents reported in recent years. The adsorption rate of expanded EPCG was 3.61 times higher than that of the previous polyantionic gel. Similarly, due to the high expansion and high permeability of EPCG, the EPCG skeleton could be further coated with an alkaline NaOH, forming a novel NaOH-coated EPCG material, and its adsorption capacity toward Cu(II) was further improved to 333.21 mg/g compared to that of pure EPCG adsorbent. Moreover, the EPCG wastes after adsorbing Cu(II) could be fully desorbed to be regenerated for reuse. A total of 99.39% of the adsorbed Cu(II) was desorbed from EPCG wastes to be recovered. The adsorption capacity of regenerated EPCG reused for adsorbing Cu(II) was 259.05 mg/g, which was very near that of the original EPCG. In addition, a series of simulation experiments and instrumental analysis were adopted to confirm the new environmental response effects as the key factors in the purification of Cu(II)-containing wastewater, including "expansion-shrink," "alkali-coating," and "acid-desorption" responses.

Cross-linked sulfydryl-functionalized graphene oxide as ultra-high capacity adsorbent for high selectivity and ppb level removal of mercury from water under wide pH range

It is highly desirable but remains extremely challenging to develop a facile strategy to prepare adsorbent for dealing with heavy metal pollution in water. Here, we report a facile approach for preparing sulfydryl-functionalized graphene oxide (S-GO) by cross-linking method with an unprecedented adsorption capacity and ultrahigh selectivity for efficient Hg(II) removal. The adsorbents exhibit a prominent performance in capturing Hg(II) from wastewater with a record-high adsorption capacity of 3490 mg/g and rapid kinetics to reduce Hg(II) contaminants below the discharge standard of drinking water (2 ppb) within 60 min under a wide pH range even in the coexistent of other interfering metal ions. In addition, the adsorbents can be also easily recycled and reused multiple times with no apparent decline in removal efficiency. Considering the broad diversity, we developed also a magnetic Fe₃O₄/S-GO adsorbent by a simple chemical cross-linking reaction to achieve rapid separation of S-GO from their aqueous solution. In addition, the adsorbents were successfully applied in dealing with the practical industrial wastewater. The results indicate the potential of rationally designed sulfydryl-functionalized graphene oxide for high performance Hg(II) removal.

Selective and efficient removal of Hg (II) from aqueous media by a low-cost dendrimer-grafted polyacrylonitrile fiber: Performance and mechanism

Polyacrylonitrile fiber was successfully modified with triazine-based dendrimer via grafting method as a promising adsorbent for removal of mercury species from aqueous media. The prepared adsorbent was characterized by elemental analysis, scanning electron microscope, Fourier transform infrared spectroscopy, porous structure analysis and X-ray photoelectron spectroscopy, providing the evidence of successful fabrication. The adsorption conditions were found via varying pH, dosage, coexisting substances, contact time, temperature and concentration. Adsorption performance, described better by the pseudo-second-order kinetics with intraparticle diffusion as rate controlling step and Langmuir isotherm model, indicated a chemisorption process with the maximum Langmuir adsorption amount of 227.64 mg g^-1 for mercury ions. Thermodynamically, adsorption of mercury ions was spontaneous and endothermic. Desorption and regeneration experiments demonstrated that it could be reused in five successive adsorption cycles without significant loss of its original performance. Experimental data and density functional theory calculation disclosed the coordination geometries and chelating mechanism between the adsorbent and mercury ions. The proposed study would provide a new prospect for the purification of mercury in aqueous system by functionalizing commercial polyacrylonitrile fiber with dendrimers.

Green chemical synthesis of new chelating fiber and its mechanism for recovery gold from aqueous solution

A novel environmentally-friendly polyacrylonitrile-2-amino-2-thiazoline chelating fiber (PANF-ATL) with good adsorption performance and thermal stability was synthesized in one step by nucleophilic addition reaction using water as a solvent. The optimum synthesis conditions for the chelating fibers are determined by controlling the synthesis temperature and the molar ratio of the reagents. The sulfur content and functional group capacity of the finally synthesized PANF-ATL were 3.82% and 1.19 mmol/g, respectively. PANF-ATL was characterized by elemental analysis, FTIR, TGA, SEM and XPS. Meanwhile, the adsorption characteristics and mechanism of PANF-ATL were evaluated. The Langmuir model and the pseudo-second-order model well described the adsorption of Au(Ⅲ) by PANF-ATL. The adsorption capacity of PANF-ATL obtained from Langmuir isotherm model towards Au(Ⅲ) was 130.58 mg/g (298 K). In addition, Au(Ⅲ) adsorbed on the fibers was completely eluted using a mixed solution of 4 mol/L HCl and 12% thiourea. It still has good adsorption performance after 5 adsorption-desorption cycles. Overall, PANF-ATL is a cost-effective adsorbent that can effectively adsorb Au(Ⅲ) in aqueous solution.

Poly(aspartic acid) Electrospun Nanofiber Hydrogel Membrane-Based Reusable Colorimetric Sensor for Cu(II) and Fe(III) Detection

Electrospun nanofiber membrane (ENM) with huge specific surface area is an ideal solid substrate for sensors. However, only a few ENMs are developed into colorimetric sensors and it is even more challenging to fabricate multiple-ion-responsive ENM-based colorimetric sensor. In this study, benefiting from the excellent metal ion adsorption ability of poly(aspartic acid) (PASP) and high specific surface area of nanofibers, a reusable colorimetric sensor utilizing PASP electrospun nanofiber hydrogel membrane (ENHM) was designed to detect Cu2+ and Fe3+ in aqueous solution with simple filtration. The sensor based on PASP-ENHM exhibited high sensitivity and selectivity, and colorimetric responses for Cu2+ and Fe3+ detection could be observed by the naked eye. Upon exposure to Cu2+ aqueous solution, the color of the sensor changed from white to blue with a naked eye detection limit of 0.3 mg/L, while it turned from white to yellow with a detection limit of 0.1 mg/L for Fe3+ detection. Furthermore, this sensor was reusable after metal ion extraction by the desorption process.

Industrial textile effluent treatment and antibacterial effectiveness of Zea mays L. Dry husk mediated bio-synthesized copper oxide nanoparticles

Zea mays L. dry husk extract was used to bio synthesize copper oxide nanoparticles. Red coloured cubic Cu₂O nanoparticles were obtained for the first time via this simple, eco- friendly, green synthesis route. The Cu₂O nanoparticles were thermally oxidized to pure monoclinic CuO nanoparticles at 600 °C. The phases of the copper oxides were confirmed from the x-ray diffraction (XRD) studies. The nanoparticle sizes as obtained from high resolution transmission electron microscope (HRTEM) analysis range from 10 to 26 nm, 36-73 nm and 30-90 nm for the unannealed Cu₂O, 300 °C and 600 °C annealed CuO respectively. The values of the bandgap energies obtained from diffuse reflectance of the nanoparticles are 2.0, 1.30 and 1.42 eV respectively for the unannealed, 300 °C, and 600 °C annealed copper oxide nanoparticles. The 600 °C annealed copper oxide nanoparticles showed 91% and 90% degradation ability for methylene blue dye (BM) and textile effluent (TE) respectively under visible light irradiation. While CuO_300 is more effective to inhibit the growth of Escherichia coli 518,133 and Staphylococcus aureus 9144, Cu₂O is better for Pseudomonas aeruginosa and Bacillus licheniformis. The results confirm the photo-catalytic and anti-microbial effectiveness of the copper oxide nanoparticles.