In situ immobilization of ultra-fine Ag NPs onto magnetic Ag@RF@Fe3O4 core-satellite nanocomposites for the rapid catalytic reduction of nitrophenols

Assembly of core-shell Fe3O4 @CD-MOFs derived hollow magnetic microcubes for efficient extraction of hazardous substances: Plausible mechanisms for selective adsorption

Hazardous heavy metals and organic substances removal is of great significance for ensuring the safety of aquatic-ecosystem, yet the highly effective and selective extraction always remains challenging. To address this problem, magnetic hollow microcubes were fabricated through thermal carbonization of Fe3O4-COOH@ γ-CD-MOFs, and core-shell structured precursors were in-situ greenly constructed on a large scale via microwave-assisted self-assembly strategy. As noted, the development of secondary crystallization was utilized to achieve uniform dispersion of cores within MOFs frameworks and thus improved magnetic and adsorption ability of composites. Acquired magnetic Fe3O4 @HC not only can harvest excellent extraction of heavy metals (Cd, Pb, and Cu of 129.87, 151.05, and 106.98 mg·g-1) but also exhibit highly selective adsorption ability for cationic organics (separation efficiency higher than 95.0 %). Impressively, Fe3O4 @HC achieved outstanding adsorption (60-80 %) of Cd in realistic mussel cooking broth with no obvious loss in amino acid. Characterizations better offer mechanistic insight into the enhanced selectivity of positively charged pollutants can be attributed to synergistic effect of ions exchange and electrostatic interaction of abundant oxygen-containing functional groups. Our study provides a feasible route by rationally developing core-shell structured composites to promote the practical applications of sustainable water treatment and value-added utilization of processing by-products.

Coupling Fe-Co atomic pair to promote the selective reduction of nitroaromatics under mild conditions

Selectively reducing nitroaromatics into aromatic amines will not only remove nitroaromatic pollutants in waste effluents to reduce environmental risks, but also yield important feedstocks for chemical industrial manufactures. In this study, a FeCo-co-embedded N-doped Carbon (FeCo-N-C) catalyst with Fe-Co atomic pair has been identified with favorable activity, superior selectivity, excellent reusability, as well as outstanding performance in the treatment of real water. The combined results from theoretical study and experimental tests indicate that the improved catalytic performance of FeCo-N-C is owing to the narrowed band gap and electron delocalization caused by the Fe-Co atomic pair which can improve electron transport in its catalytic reaction. The results of isotope experiments and H* quenching experiments confirm that H2O is the source of hydrogen in catalytic reduction of PNP. FeCo-N-C is identified as a superior catalyst to replace multitudinous currently used noble-metal catalysts for the selective catalytic reduction of nitroaromatics in wastewater treatment.

Na2Ti3O7@RF@Ag Heterostructures as Efficient Substrates for SERS and Photocatalytic Applications

A multi-step procedure was effectively employed to synthesize innovative three-dimensional (3D) heterostructures encompassing sodium titanate (Na2Ti3O7) nanowire cores, an intermediate resorcinol-formaldehyde (RF) layer, and outer silver (Ag) nanoparticle sheaths, referred to as Na2Ti3O7@RF@Ag heterostructures. Initially, a one-step hydrothermal technique facilitated the direct growth of single-crystal Na2Ti3O7 nanowires onto a flexible Ti foil. Subsequently, a two-step wet chemical process facilitated the sequential deposition of an RF layer and Ag nanoparticles onto the Na2Ti3O7 nanowires at a low reaction temperature. Optimal concentrations of silver nitrate and L-ascorbic acid can lead to the cultivation of Na2Ti3O7@RF@Ag heterostructures exhibiting heightened surface-enhanced Raman scattering (SERS), which is particularly beneficial for the detection of rhodamine B (RhB) molecules. This phenomenon can be ascribed to the distinctive geometry of the Na2Ti3O7@RF@Ag heterostructures, which offer an increased number of hot spots and surface-active sites, thereby showcasing notable SERS enhancement, commendable reproducibility, and enduring stability over the long term. Furthermore, the Na2Ti3O7@RF@Ag heterostructures demonstrate remarkable follow-up as first-order chemical kinetic and recyclable photocatalysts for the photodecomposition of an RhB solution under UV light irradiation. This result can be attributed to the enhanced inhibition of electron-hole pair recombination and increased surface-active sites.

Microwave-assisted one-pot preparation of magnetic cactus-derived hydrochar for efficient removal of lead(Ⅱ) and phenol from water: Performance and mechanism exploration

A novel magnetic hydrochar derived from cactus cladode (MW-MHC) was successfully synthesized through one-pot microwave-assisted process for efficiently removing lead(Pb)(Ⅱ) and phenol. From batch adsorption experiments, MW-MHC possessed the highest uptake amounts for Pb(Ⅱ) and phenol of 139.34 and 175.32 mg/g within 20 and 60 min, respectively. Moreover, the removal of Pb(Ⅱ) and phenol by MW-MHC remained essentially stable under the interference of different co-existing cations, presenting the excellent adaptability of MW-MHC. After three cycles of regeneration experiments, MW-MHC still had preferable adsorption performance and could be easily recycled, indicating its excellent reusability. Significantly, the uptake mechanisms of Pb(Ⅱ) on MW-MHC were regarded as chemical complexation, pore filling, precipitation, and electrostatic attraction. Meanwhile, the phenol uptake might be dominated by π-π interaction and hydrogen bonding. The above consequences revealed that MW-MHC with high removal performance was a promising adsorbent for remediating wastewater containing heavy metals and organics.

Improved recovery selectivity of rare earth elements from mining wastewater utilizing phytosynthesized iron nanoparticles

While rare earth elements (REEs) play key roles in many modern technologies, the selectivity of recovering of REEs from mining wastewater remains a critical problem. In this study, iron nanoparticles (FeNPs) synthesized from euphorbia cochinchinensis extracts were successfully used for selective recovery of REEs from real mining wastewater with removal efficiencies of 89.4% for Y(III), 79.8% for Ce(III) and only 6.15% for Zn(Ⅱ). FTIR and XPS analysis suggested that the high selective removal efficiency of Y(III) and Ce(III) relative to Zn(Ⅱ) on FeNPs was due to a combination of selective REEs adsorption via complexing with O or N, ion exchange with H+ present in functional groups contained within the capping layer and electrostatic interactions. Adsorptions of Y(III) and Ce(III) on FeNPs conformed to pseudo second-order kinetics and the Langmuir isotherm model with maximum adsorption capacities of 5.10 and 0.695 mg∙g-1, respectively. The desorption efficiencies of Y(III) and Ce(III) were, respectively, 95.0 and 97.9% in 0.05 M acetic acid, where desorption involved competitive ion exchange between Y(III), Ce(III) and Zn(Ⅱ) with H+ contained in acetic acid and intraparticle diffusion. After four consecutive adsorption-desorption cycles, adsorption efficiencies for Y(III) and Ce(III) remained relatively high at 52.7% and 50.1%, respectively, while desorption efficiencies of Y(III) and Ce(III) were > 80.0% and 95.0%, respectively. Overall, excellent reusability suggests that FeNPs can practically serve as a potential high-quality selectivity material for recovering REEs from mining wastewaters.

Pd nanoparticles anchored Co-MOF for nitrophenol reduction

Three nitrophenols are among the 126 priority toxic pollutants identified by the US Environmental Protection Agency. Catalyzing hydrogenation is a simple way to convert these toxic nitrophenols into harmless aminophenols. Commercial PdC has excellent catalytic hydrogenation activity but has weaknesses such as high price and low reusability. Here, we fabricated a series of nano-Pd 2D Co-MOF heterostructures and filtered for optimal Co-MOF@Pd0.0012, which contain ultra-low Pd content (0.08 wt%) and recorded high catalytic efficiency for 4-nitrophenol among the reported non-single atom catalyst due to edge and size effects. The TOF value of Co-MOF@Pd0.0012 is 9800 h-1, ∼206 times higher than that of PdC (Pd content, 10 wt%). Furthermore, Co-MOF@Pd0.0012 has been widely applied to catalyze the reduction of various nitrophenol substrates with higher than 99% conversion efficiency and selectivity.

Palladium nanoparticles supported on ionic liquid and glucosamine-modified magnetic iron oxide as a catalyst in reduction reactions

A magnetic nanocomposite comprising imidazolium ionic liquid and glucosamine is successfully synthesized and used for stabilization of Pd nanoparticles. This new material, Fe₃O₄@SiO₂@IL/GA-Pd, is fully characterized and applied as a catalyst in the reduction of nitroaromatic compounds to desired amines at room temperature. Also, the reductive degradation of organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) is studied and compared with another previous publications. The survey of the stabilization of the palladium catalytic entities is described demonstrating the separation ability and recycling of them. In addition, TEM, XRD, and VSM analyses of the recycled catalyst confirmed its stability.

One-step self-assembly of Fe-biochar composite for enhanced persulfate activation to phenol degradation: Different active sites-induced radical/non-radical mechanism

Persulfate (PS) activation by nanoscale zerovalent iron (nZVI) is promising for water purification, while is limited due to its easy agglomeration and oxidation. Herein, nZVI encapsuled in carbon matrix shell was synthesized via one-step carbothermal reduction. The core-shell structure effectively inhibited oxidation and agglomeration of nZVI core, and graphitized porous structures facilitated phenol binding with maximal adsorption capacity of 117.10 mg/g achieved by nZVI_0.6-BC₈₀₀. Both reactive oxygen species (SO₄^•-, O•H, O₂^•- and ¹O₂) and electron transfer process resulted in phenol decomposition. Owing to diversified active sites, the nZVI_0.6-BC₈₀₀/PS system could completely degrade phenol degradation within short time, and exhibited great adaptation to extensive pH range (3.0-9.0) and coexisting substances. Additionally, the nZVI_0.6-BC₈₀₀/PS system could maintain over 85% removal of phenol after three recycles or 50 days of storage, and was highly-efficient to different water environments, thus proposing rational design of iron-carbon catalyst with potential in water treatment.

Wastewater treatment: A universal, scalable and recyclable catalyst with adjustable activity for diverse dyes degradation

The growing concern over water shortage and pollution is propelling and accelerating the development of sewage treatment technologies. Among them, the catalytic hydrogenation method is highly recommended from a sustainable perspective, because it can turn toxic pollutants into valuable raw materials. The catalyst with excellent activity and stability plays a critical role in this "trash to treasure" approach. Herein, we proposed a novel economical, scalable and recyclable candidate catalyst, i.e., the copper nanoparticles supported on zinc oxide nanowire array (Cu-ZnO NWA), for realizing efficient and stable dye wastewater treatment. The salix argyracea-shaped Cu-ZnO NWA displays very outstanding universality and controllability towards the catalytic hydrogenation reactions of diverse dyes, owing to the fact that ZnO nanowire array not only offers a platform to realize stable and homogeneous dispersion of Cu nanoparticles, but also provides a large quantity of catalytically active sites. More attractively, its synthetic method can be facilely extended to various conductive substrates through combined electrodeposition and hydrothermal technique, showing its general applicability for the surface assembly of sewage treatment facilities. Benefiting from above advantages, this proposal offers an attractive approach for large-scale and continuous decolorization of dye wastewater, and presents a broad application prospect in the textile printing industry.

In Situ Implantation of Bi2S3 Nanorods into Porous Quasi-Bi-MOF Architectures: Enabling Synergistic Dissociation of Borohydride for an Efficient and Fast Catalytic Reduction of 4-Nitrophenol

Catalytic hydrogenation reduction based on sodium borohydride (NaBH₄) has gained attention as an appealing "one-stone-two-birds" approach for the simultaneous elimination of nitroaromatic pollutants and the production of high-value aminoaromatics under mild conditions. However, the slow kinetics of NaBH₄ dissociation on the surface of catalysts restrict the catalytic hydrogenation reduction efficiency. Herein, we report an intelligent localized sulfidation strategy for an in situ implantation of Bi₂S₃ nanorods within quasi-Bi-MOF architectures (Bi₂S₃@quasi-Bi-MOF) by fine-tuning the pyrolysis temperature. In this novel Bi₂S₃@quasi-Bi-MOF, the porous quasi-Bi-MOF enables efficient adsorption of BH₄^- and 4-nitrophenol (4-NP), while Bi₂S₃ facilitates the BH₄^- dissociation to form H_ads* species adsorbed on the catalyst surface. Benefiting from the synergistic structure, Bi₂S₃@quasi-Bi-MOF exhibits excellent performance for the catalytic reduction of 4-NP, delivering a high turnover frequency (TOF) of 1.67 × 10^-4 mmol mg^-1 min^-1 and an extremely high normalized rate constant (k_nor) of 435298 s^-1 g^-1. The kinetic analysis and electrochemical tests indicate that this catalytic hydrogenation reduction follows the Langmuir-Hinshelwood mechanism. This study enriches the synthetic strategy of MOF-based derivatives and offers a new catalytic platform for hydrogenation reduction reactions.

Hydrothermal carbonization of alfalfa: role of processing variables on hydrochar properties

Hydrothermal carbonization of alfalfa is a potential way to reuse agricultural waste. However, the effects of hydrothermal conditions on the properties of alfalfa-derived hydrochar are not clear. Herein, this study investigated the impact of different synthesis conditions (e.g., heating temperature, heating time, and solid to liquid ratio) on the formation and properties of hydrochar. Characterization and thermogravimetric analysis results revealed that with the increase of hydrothermal temperature and the extension of time, cellulose in alfalfa broken down more completely, and the number of carbon spheres and the aromatization degree increased, while the functional groups decreased. Furthermore, there was a surge in the carbon content, fixed carbon yield, high heating value, reduced oxygen, and volatile content. Additionally, the enhancement solid-liquid ratio could effectively improve the energy and mass yields. In all, by adjusting the process parameters of hydrochar, cleaner and higher productivity products could be obtained. This study provides theory basis for the production of target hydrochar that is used to soil amendments, adsorbents, and energy sources in the future.

Recyclable Mussel-Inspired Magnetic Nanocellulose@Polydopamine-Ag Nanocatalyst for Efficient Degradation of Refractory Organic Pollutants and Bacterial Disinfection

Development of a novel strategy to tackle bacterial-contaminated complex industrial wastewaters containing refractory organic pollutants is of great demand. In this study, polydopamine (PDA)-coated magnetic cellulose nanofiber (MCNF)-loaded silver nanoparticle (AgNP) (MCNF/PDA-Ag) nanocomposites were designed and applied for efficient degradation of organic dye pollutants and inactivation of Escherichia coli (E. coli) in wastewater. In the presence of NaBH₄, MCNF/PDA-Ag could achieve a high catalytic reduction rate of 6.54 min^-1 for the removal of methylene blue. Similarly, it showed good catalytic reduction performance for methyl orange (0.63 min^-1) and 4-nitrophenol (2.94 min^-1). The MCNF/PDA-Ag nanocomposites can be easily magnetically recycled and reused with negligible loss of catalytic performance. Moreover, this nanocatalyst also exhibited excellent disinfection performance against E. coli, with more than 99% disinfection ratio at very low doses (50 μg/mL). Overall, this work provides new insights into a delicate design of advanced magnetically recyclable silver nanocomposites with ultrahigh catalytic rates and excellent antibacterial properties from sustainable nature biomass.

Polyethylenimine-grafted nitrogen-doping magnetic biochar for efficient Cr(VI) decontamination: Insights into synthesis and adsorption mechanisms

Herein, polyethylenimine (PEI)-grafted nitrogen (N)-doping magnetic biochar (PEI_MW@MNBC_BM) was synthesized, and characterization results showed that the microwave-assisted PEI grafting and ball milling-assisted N doping introduced abundant amino, pyridine N and pyrrole N structures onto biochar, which possessed high affinity to Cr(VI) in the anion form. The as-prepared PEI_MW@MNBC_BM displayed pH-dependence adsorption performance and high tolerance to co-existing ions with maximum uptake capacity of Cr(VI) identified as 183.02 mg/g. Furthermore, PEI_MW@MNBC_BM could bind Cr(VI) through electrostatic attraction, complexion, precipitation, reduction and pore filling. Especially, effective reduction of Cr(VI) was ascribed to cooperative electron transfer of partial oxygen-containing functional groups, intramolecular pyridine/pyrrole N, protonated amino and Fe²⁺ on the adsorbent, while oxygen-containing and amino functional groups from N-doping biochar and PEI synergistically complexed Cr(III) via providing lone pair electrons to form coordinate bonds. Furthermore, the stable precipitation was formed between Fe³⁺ and Cr(III). Additionally, the Cr(VI) elimination efficiency could maintain 95.83% even after four adsorption-desorption cycles, suggesting PEI_MW@MNBC_BM as a high-performance adsorbent for Cr(VI) contaminated water remediation.

Bacterial-driven upcycling spent Ag into high-performance catalyst for toxic organics reduction

Achieving up-cycling and reusing of silver from the waste X-rays films is currently a huge challenge. Here, we designed a facile method that upcycles Ag⁺ extract efficiently from waste film into highly dispersed value-added biological Ag/AgO-AgCl nanoparticles (bio-Ag/AgO-AgCl NPs) using Bacillus thuringiensis-secreted extracellular polymeric substance without additional reductants and electron donors. The recovery efficiency of silver exceeded 99.8%. Surprisingly, the bio-Ag/AgO-AgCl NPs can well solve the bottleneck problem of slow Ag catalytic kinetics. When the amount of catalyst was 1.9 mg, the reduction efficiency and reduction rate of 10 ppm methyl orange were 97.9% and 7 min, and that of 30 ppm Congo red were 95.3% and 5 min respectively, which is superior to other chemically synthesized silver-base catalysts. This bioremediation methodology provides an effective and practical technical approach for precious metal remediation and sustainable energy development.

Two-step ball milling-assisted synthesis of N-doped biochar loaded with ferrous sulfide for enhanced adsorptive removal of Cr(Ⅵ) and tetracycline from water

Nitrogen-doped biochar loaded with FeS (FeS@NBC_BM) was synthesized by two-step ball milling processes. Characterization results revealed that N-doping process successfully introduced pyridinic, pyrrolic, and graphitic N structures, and FeS was subsequently embedded in N-doped biochar (NBC_BM). The resultant FeS@NBC_BM presented predominant adsorption capacity for Cr(VI) (194.69 mg/g) and tetracycline (TC, 371.29 mg/g) compared with BC (27.28 and 37.89 mg/g) and NBC_BM (71.26 and 81.26 mg/g). In addition, the Cr(VI)/TC elimination process by FeS@NBC_BM was basically stable with multiple co-existing ions with slight decrease on adsorption performance after three desorption-regeneration cycles. Most importantly, FeS@NBC_BM was found to achieve Cr(VI) elimination not only by electrostatic attraction, ion exchange and complexation, but also by electrons-triggered reduction provided by different species of N, Fe²⁺ as well as S(Ⅱ). Meantime, pore filling, hydrogen bonding, and π-π stacking interactions were demonstrated to contribute to TC adsorption. These results suggested the co-modification of N-doping and FeS loading by ball milling as an innovative decorating method for biochar to adsorptive purification of Cr(VI) and TC-contaminated water.

Swift reduction of nitroaromatics by gold nanoparticles anchored on steam-activated carbon black via simple preparation

Gold (Au) nanoparticles supported on certain platforms display highly efficient activity on nitroaromatics reduction. In this study, steam-activated carbon black (SCB) was used as a platform to fabricate Au/SCB composites via a green and simple method for 4-nitrophenol (4-NP) reduction. The obtained Au/SCB composites exhibit efficient catalytic performance in reduction of 4-NP (rate constant k_app = 2.1925 min^-1). The effects of SCB activated under different steam temperature, Au loading amount, pH, and reaction temperature and NaBH₄ concentration were studied. The structural advantages of SCB as a platform were analyzed by various characterizations. Especially, the result of N₂ adsorption-desorption method showed that steam activating process could bring higher surface area (from 185.9689 to 249.0053 m²/g), larger pore volume (from 0.073268 to 0.165246 cm³/g), and more micropore for SCB when compared with initial CB, demonstrating the suitable of SCB for Au NP anchoring, thus promoting the catalytic activity. This work contributes to the fabrication of other supported metal nanoparticle catalysts for preparing different functional nanocomposites for different applications.

Green synthesis of Ag nanoparticles using elm pod polysaccharide for catalysis and bacteriostasis

The green synthesis of silver nanoparticles (Ag NPs) for catalysis and biological applications has gained great interest. Natural elm pods are a type of food that possesses anti-inflammatory and pain-relieving effects. In this study, elm pod polysaccharide (EPP) was extracted from elm pods using hot water extraction for the first time. Biocompatible EPP-stabilized silver nanoparticles (EPP-Ag_n NPs) were prepared by using a green synthesis method. The EPP-Ag₂₅ NPs had a hydrodynamic size of 40.9 nm and a highly negative surface charge of -27.4 mV. Furthermore, EPP-Ag₂₅ NPs exhibited high catalytic activity for the reduction of 4-nitrophenol, and the catalytic reaction followed a pseudo-first order kinetic equation. More importantly, the inhibition rate of EPP-Ag₂₅ NPs on Escherichia coli was 71 % when samples were treated with an 808 nm laser. Besides, EPP-Ag_n NPs effectively inhibited the proliferation of tumor cells irradiated by an 808 nm laser. The improved performance of EPP-Ag_n NPs was due to the good stability of EPP. Taken together, EPP-Ag_n NPs had good stability, catalytic activity, antibacterial and antitumor ability under laser irradiation. EPP is a good stabilizer for many nanoparticles which have broad applications in the field of catalysis and biomedicine in the future.

Gum Hydrocolloids Reinforced Silver Nanoparticle Sponge for Catalytic Degradation of Water Pollutants

The accumulation of organic contaminants including dyes in aquatic systems is of significant environmental concern, necessitating the development of affordable and sustainable materials for the treatment/elimination of these hazardous pollutants. Here, a green synthesis strategy has been used to develop a self-assembled gum kondagogu-sodium alginate bioconjugate sponge adorned with silver nanoparticles, for the first time. The properties of the nanocomposite sponge were then analyzed using FTIR, TGA, SEM, and MicroCT. The ensued biobased sponge exhibited hierarchical microstructure, open cellular pores, good shape memory, and mechanical properties. It merges the attributes of an open cellular porous structure with metal nanoparticles and are envisaged to be deployed as a sustainable catalytic system for reducing contaminants in the aqueous environment. This nanocomposite sponge showed enhanced catalytic effectiveness (k_m values up to 37 min⁻¹ g⁻¹ and 44 min⁻¹ g⁻¹ for methylene blue and 4-nitrophenol, respectively), antibacterial properties, reusability, and biodegradability (65% biodegradation in 28 days).

Synthesis of Biogenic Silver Nanocatalyst and their Antibacterial and Organic Pollutants Reduction Ability

Plant-mediated nanoparticles are gaining popularity due to biologically active secondary metabolites that aid in green synthesis. This study describes a simple, environmentally friendly, dependable, and cost-effective production of silver nanoparticles utilizing Cucumis sativus and Aloe vera aqueous leaf extracts. The aqueous leaf extracts of Cucumis sativus and Aloe vera, which worked as a reducing and capping agent, were used to biosynthesize silver nanoparticles (AgNPs). The formation of surface plasmon resonance peaks at 403 and 405 nm corresponds to the formation of colloidal Ag nanoparticles. Similarly, the Bragg reflection peaks in X-ray diffraction patterns observed at 2θ values of 38.01°, 43.98°, 64.24°, and 77.12° representing the planes of [111], [200], [220], and [311] correspond to the face-centered cubic crystal structure of silver nanoparticles. Fourier transform infrared spectroscopy confirms that bioactive chemicals are responsible for the capping of biogenic silver nanoparticles. The size, structure, and morphology of AgNPs with diameters ranging from 8 to 15 nm were examined using transmission electron microscopy. Water contamination by azo dyes and nitrophenols is becoming a more significant threat every day. The catalytic breakdown of organic azo dye methyl orange (MO) and the conversion of para-nitrophenol (PNP) into para-aminophenol using sodium borohydride was evaluated using the prepared biogenic nanoparticles. Our nanoparticles showed excellent reduction ability against PNP and MO with rate constants of 1.51 × 10^-3 and 6.03 × 10^-4s^-1, respectively. The antibacterial activity of the nanomaterials was also tested against four bacteria: Staphylococcus aureus, Klebsiella pneumoniae, Enterobacter, and Streptococcus pneumoniae. These biogenic AgNPs displayed effective catalytic and antibacterial characteristics by reducing MO and PNP and decreasing bacterial growth.

Ag nanoparticles anchored on NiO octahedrons (Ag/NiO composite): An efficient catalyst for reduction of nitro substituted phenols and colouring dyes

The development of an efficient sustainable catalyst for effective removal of hazardous chemicals, viz. nitrophenols and organic dyes, from wastewater is a challenging task. Herein, facile synthesis of Ag/NiO composites by anchoring Ag nanoparticles (NPs) on NiO octahedrons with different amounts of Ag NPs (AN-5% (5% Ag), AN-10% (10% Ag) and AN-15% (15% Ag)) has been demonstrated. SEM (scanning electron microscopic) and TEM (transmission electron spectroscopic) images ensured the proper anchoring of spherical Ag NPs (particle size = 16.54 ± 1.88 nm) on octahedron particles of NiO, which was also ensured by XPS (X-ray photoelectron spectroscopy) analysis. Moreover, the resulting composites have an average surface area (49-52 m²g^‒1) and pore size (2.39-2.26 nm). All three synthesized Ag/NiO composites (100 μL) catalyzed the complete reduction of para-np (4-nitrophenol: 0.1587 mM) within 2-3 min in the presence of 0.04 M NaBH₄. Among them, AN-5% has been chosen because of the lowest anchored Ag (5%) to obtain the optimized catalyst's amount (50 μL) and concentration of para-np (0.1587 mM). AN-5% also exhibited excellent catalytic activity towards different nitro substituted phenols, viz. ortho-np (2-nitrophenol), meta-np (3-nitrophenol), para-np (4-nitrophenol) and tri-np (2,4,6-trinitrophenol). AN-5% displayed ∼100% catalytic efficiency for reducing meta-np in 2 min with the apparent first order rate constant (k_app) and normalized rate constant (K_nor) as 1.99 s^-1 and 398.14 s^-1 g^-1, respectively. Additionally, AN-5% (29.41 μg mL^-1) reduced >95% of the colouring dyes (10 ppm) such as CONG-R (congo red: 95% in 6 min), METH-O (methyl orange: 97.5% in 7 min), METH-B (methylene blue: 98.3% in 10 min) and RHOD-B (rhodamine B: 99.2% in 5 min). AN-5% not only demonstrated catalytic reduction towards individual pollutants, but also showed excellent activity for reduction of the mixtures of nitrophenols/dyes and for treatment of simulated industrial effluent samples (EFF1, EFF2) and a real industrial sample (textile dye-bath effluent). AN-5% can also be reused up to several cycles with almost same efficiency and followed the Langmuir-Hinshelwood apparent first order kinetics model.

Zwitterionic peptide-functionalized highly dispersed carbon nanotubes for efficient wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) have displayed great potential as catalyst carriers due to their nanoscale structure and large specific surface area. However, their hydrophobicity and poor dispersibility in water restrict their applications in aqueous environments. Herein, the dispersibility of MWCNTs was significantly enhanced with a chimeric protein MPKE which consisted of a zwitterionic peptide unit and a mussel adhesive protein unit. The MPKE could be easily attached to MWCNTs (MPKE-MWCNTs) by a simple stirring process due to the versatile adhesion ability of mussel adhesive unit. As expected, the MPKE-MWCNTs displayed outstanding dispersibility in water (>7 months), as well as in alkaline solutions (pH = 12) and organic solvents (DMSO and ethanol) due to the hydrophilicity of the zwitterionic peptide unit. Moreover, the MPKE-MWCNTs were used as silver nanoparticle carriers for the reduction of 4-nitrophenol in wastewater, with the normalized rate constant k_nor up to 32.9 s^-1 mmol^-1. Meanwhile, they also exhibited excellent biocompatibility and antibacterial activity, which were favorable for wastewater treatment. This work provides a facile strategy for MWCNT modification, functionalization and applications in aqueous environments.

Mussel-Inspired Ag NPs Immobilized on Melamine Sponge for Reduction of 4-Nitrophenol, Antibacterial Applications and Its Superhydrophobic Derivative for Oil-Water Separation

A functional material integrated with a variety of functions is highly desired in wastewater treatment. In this research, a mussel-inspired method of immobilizing silver nanoparticles on the skeleton of a melamine sponge is proposed and applied for water remediation. Ag NPs were reduced in situ and grown on a polydopamine-modified melamine sponge. The catalytic reduction of 4-nitrophenol (4-NP) in the presence of the obtained MS-PDA-Ag was evaluated, and the results demonstrated that the MS-PDA-Ag presented high catalytic reduction activity. In addition, the monolithic MS-PDA-Ag presents excellent reusability with no remarkable decrease in catalytic efficiency after multiple reuses. Owing to the immobilized Ag NPs, the MS-PDA-Ag can also effectively inhibit the growth of bacteria against both gram-positive and gram-negative species, making it possible for bacteria elimination in polluted water. To further explore the possibility of utilizing the MS-PDA-Ag for versatile applications, a superhydrophobic derivative (S-MS-PDA-Ag) was prepared by coating a low-surface-energy substance (octadecanethiol) on the surface of MS-PDA-Ag. The obtained S-MS-PDA-Ag presents the capacities of oil/organics adsorption and water repellence, which can separate the insoluble oil/organics from water. The melamine sponge immobilized with Ag NPs demonstrates prominent catalytic reduction of 4-NP, antibacterial activity and the superhydrophobic derivative presents the capacity of insoluble oil/organics separation from oil-water mixtures, exhibiting high potential in the remediation of polluted water.

Superhydrophilic three-dimensional porous spent coffee ground reduced palladium nanoparticles for efficient catalytic reduction

The use of functional biodegradable wastes to treat environmental problems would create minimal extra burden to our environment. In this paper, we propose a sustainable and practical strategy to turn spent coffee ground (SCG) into a multifunctional palladium-loaded catalyst for water treatment instead of going into landfill as solid waste. Bleached delignified coffee ground (D-SCG) has a porous structure and a good capability to reduce Pd (II) to Pd (0). A large amount of nanocellulose is formed on the surface of SCG after bleaching by H₂O₂, which anchors and disperses the palladium nanoparticles (Pd NPs). The D-SCG loaded with Pd NPs (Pd-D-SCG) is superhydrophilic, which facilitates water transport and thus promotes efficient removal of organic pollutants dissolved in water. Pd-D-SCG exhibits excellent room temperature catalytic activity for the removal of 4-nitrophenol (4-NP) and methylene blue (MB) in water and shows good chemical stability and recyclability in water, with no obvious decrease even after five repeated cycles.

Highly efficient catalytic hydrogenation of nitrophenols by sewage sludge derived biochar

Finding a low cost and effective alternative to noble metal based catalyst has long been concerned in wastewater treatment and organic transformation. This work developed a highly efficient sewage sludge-based catalyst via a simple one-step pyrolysis method, and for the first time, applied it in the catalytic reduction of nitrophenols. Due to the higher content of graphitic nitrogen, abundant defect sites and low electron transfer resistance, sewage sludge derived biochar obtained at 800 °C (SSBC-800) exhibits the best catalytic performance, with the reaction rate of 0.48 min^-1 and turnover frequency for 4-nitrophenol calculated to be 1.25 × 10^-4 mmol•mg^-1 min^-1, which is comparable to or even superior than some reported noble metal-based catalyst. Moreover, SSBC-800 showed good recyclability of 90% 4-nitrophenol removal within 8 min after 4 runs, and maintained high catalytic activity in reduction of other substituent nitrophenols, such as 2-nitrophenol (0.54 min^-1), 3-nitrophenol (0.61 min^-1) and 2,4-dinitrophenol (0.18 min^-1), and in real water samples, indicating its practical applicability. The electron paramagnetic resonance spectra and electrochemical characterization demonstrate that SSBC-800 accelerates the dissociation of BH₄^- to form active hydrogen, which is the main species responsible for 4-nitrophenol reduction, while electron transfer reaction involving the surface bound hydride derived from the intimate contact between BH₄^- and SSBC-800 plays an important role in this process. This research not only provides a novel valorization pathway for sewage sludge, but also sheds new light on further designing of carbon-based catalyst for nitrophenol reduction.

Design, Fabrication and Applications of Electrospun Nanofiber-Based Surface-Enhanced Raman Spectroscopy Substrate

Surface-enhanced Raman spectroscopy (SERS) is an advanced and powerful analysis tool. Due to the advantages of high sensitivity, high resolution, and nondestructive testing, it has been widely used in physics, chemistry, material science and other fields. In recent years, substantial progress has been made in developing flexible platforms for the design and fabrication of SERS substrates. One important kind of the flexible platforms is based on electrospun nanofibers. Electrospun nanofibers not only have unique advantages such as easy preparation, high porosity and large specific surface area, but also can increase the number of hotspots when combined with precious metal nanomaterials, thereby enhancing the SERS signal and expanding the application scope. In this review, we firstly focus on two strategies for the fabrication of metal nanostructure decorated in/on the electrospun nanofibers, namely in-situ and ex-situ. Then the applications of these SERS substrates in the fields of quantitative analysis, monitoring chemical reactions and recyclable detection are introduced in detail. Finally, the challenges as well as perspectives are presented to offer a guideline for the future exploration of these SERS substrates. We expect that it will provide new inspiration for the development of electrospun nanofiber-based SERS substrates.

Biochar-mediated reduction of m-nitrotoluene: Interaction between reduction of m-nitrotoluene and sequestration of contaminants

Biochar is a highly effective adsorbent for nitroaromatic compounds (NACs), and acts as an electron shuttle that mediates the reduction of NACs. Hence, when biochar is used to mediate NAC reduction, adsorption and reduction will occur simultaneously and affect each other. However, the effect of biochar-mediated NAC reduction on sorption remains unknown. Eight biochars with different physicochemical properties were used to adsorb m-nitrotoluene and mediate its reduction. The results showed that the adsorption of m-nitrotoluene onto the various biochars facilitated its reduction, whereas biochar-mediated reduction retarded and weakened contaminant adsorption, which increased the environmental risk posed by m-nitrotoluene. Nevertheless, biochars with a high graphitization degree and developed porosity not only had a great catalytic ability, but also significantly alleviated the negative effect of reduction on adsorption. This was ascribed to the π-π interaction and pore-filling effect, which played more important roles than the hydrophobic effect in adsorbing the reduction product (m-toluidine) onto the studied biochars during reduction. Furthermore, the methanol extraction results indicated that the eight biochars presented significantly stronger sequestration abilities for adsorbed m-toluidine than for adsorbed m-nitrotoluene. This resulted from the hydrogen bonding and the Lewis acid-base effect between m-toluidine and each biochar, which were absent for m-nitrotoluene. These results suggest that biochars with a high graphitization degree and developed porosity are applicable for mediating reduction-enhancing sequestration of NACs, which could be a novel strategy for NAC remediation.

Two-dimensional ultrathin surfactant-encapsulating polyoxometalate assemblies as carriers for monodispersing noble-metal nanoparticles with high catalytic activity and stability

Noble metal nanoparticles (NMNPs) with excellent catalytic activity and stability play an important role in the field of environmental governance. A uniform distribution and a strong binding force with the carriers of the noble metal nanoparticles are important, but avoidance of the use of additional reducing agents is a promising direction of research. Herein, 2D ultrathin surfactant-encapsulating polyoxometalate (SEP) nanosheets constructed by the self-assembly of dodecyldimethylammonium bromide (DODA) and molybdophosphate (H3PMo12O40, PMo12) are designed to be versatile carriers for Ag nanoparticles. Under the synergistic effect of the well-arranged PMo12 units, encapsulating hydrophobic oleic acid (OA) and reductive molybdophosphate under Xe lamp irradiation, the silver oleate (AgOA)-derived Ag nanoparticles (5 ± 2 nm) are monodispersed on the DODA-PMo12 assemblies and form the Agx/DODA-PMo12 composite. The optimized Ag4.89/DODA-PMo12 composite exhibits high catalytic activity and stability in the degradation of 4-nitrophenol (4-NP), which reaches a superior rate constant of 6.49 × 10-3 s-1 and without significant deterioration after three recycles. This technique can be facilely promoted to other noble metal nanoparticles with excellent catalytic activity and stability.

Highly Efficient Silver Catalyst Supported by a Spherical Covalent Organic Framework for the Continuous Reduction of 4-Nitrophenol

Developing new materials and novel technologies for the highly efficient treatment of toxic organic pollutants is highly desirable. Chemical reduction based on heterogeneous substrate/noble metal catalysts and the reducing agent NaBH₄ has become an effective method in recent years. Here, a spherical covalent organic framework (SCOF) was designed to provide basic sites for Ag ions, by which small Ag NPs were immobilized on the SCOF to form Ag NPs@SCOF microspheres. The prepared microspheres exhibited a high catalytic reduction ability toward 4-nitrophenol (4-NP). An optimized permeation flux of 2000 L m^-2 h^-1 (LMH) and a more than 99% 4-NP reduction efficiency were obtained with flow-through experiments, which are far better than the reported results (below 200 LMH). Moreover, the microspheres could maintain stable catalytic performance under a continuous flow-through process. Our work provides an efficient material and technology that can be applied to easily treat toxic organic pollutants.