A one step synthesis of hybrid Fe/Ni-rGO using green tea extract for the removal of mixed contaminants

Magnetically recoverable Ni-doped iron oxide/graphitic carbon nitride nanocomposites for the improved photocatalytic degradation of ciprofloxacin: Investigation of degradation pathways

Developing efficient and effective photocatalysts is essential for organic dyes and antibiotic degradation in wastewater. Ni-doped α-Fe2O3/g-C3N4 (NFGCN) photocatalysts were synthesised through a simple co-precipitation technique and used for the ciprofloxacin (CIP) and methylene blue (MB) degradation through photocatalysis. The XRD data indicated the crystallinity of the synthesised iron oxide and its composites with rhombohedral structures with the nature of high purity. The morphology of the NFGCN composite revealed the construction of Ni-doped α-Fe2O3 (NFO) nanoparticles onto the g-C3N4 (GCN) sheet surface along with the close interface that induced a Z-scheme heterojunction. The synthesised photocatalysts showed photocatalytic activity with good degradation efficiency of 82.1 % and 92.0 % for CIP and MB, respectively, within 120 min under solar light exposure. The improved photocatalytic degradation efficiency was attained owing to the synthesised composite's enhanced light absorption in the visible range. The narrow band gap energies and interaction between Ni-doped α-Fe2O3 and g-C3N4 displayed by these materials result in enhanced visible light absorption, effective charge carrier separation and transportation to the pollutants. CIP degradation pathways were investigated utilising the LC-MS analysis. NFGCN composites showed good recyclability (5 cycles), magnetic retrievability, and stability for degrading organic and emerging pollutants from wastewater through photocatalysis.

Facile Fabrication of Nickel Supported on Reduced Graphene Oxide Composite for Oxygen Reduction Reaction

Due to the depletion of fossil fuels, the demand for renewable energy has increased, thus stimulating the development of novel materials for energy conversion devices such as fuel cells. In this work, nickel nanoparticles loaded on reduced graphene oxide (Ni/rGO) with small size and good dispersibility were successfully prepared by controlling the pyrolysis temperature of the precursor at 450 °C, assisted by a microwave-assisted hydrothermal method, and exhibited enhanced electrocatalytic activity towards oxygen reduction reaction (ORR). Additionally, the electron enrichment on Ni NPs was due to charge transfer from the rGO support to metal nickel, as evidenced by both experimental and theoretical studies. Metal-support interactions between nickel and the rGO support also facilitated charge transfer, contributing to the enhanced ORR performance of the composite material. DFT calculations revealed that the first step (from O2 to HOO*) was the rate-determining step with an RDS energy barrier lower than that of the Pt(111), indicating favorable ORR kinetics. The HOO* intermediates can be transferred onto rGO by the solid-phase spillover effect, which reduces the chemical adsorption on the nickel surface, thereby allowing continuous regeneration of active nickel sites. The HO2- intermediates generated on the surface of rGO by 2e- reduction can also efficiently diffuse towards the nearby Ni surface or the interface of Ni/rGO, where they can be further rapidly reduced to OH-. This mechanism acts as the pseudo-four-electron path on the RRDE. Furthermore, Ni/rGO-450 demonstrated superior stability, methanol tolerance, and durability compared to a 20 wt% Pt/C catalyst, making it a cost-effective alternative to conventional noble metal ORR catalysts for fuel cells or metal-air batteries.

Enhanced activity of Fe/Mn nanoparticles using a response surface methodology and mechanism for removing oxytetracycline and copper ion

As feed additives, oxytetracycline (OTC) and copper ion (Cu(II)) are often detected in livestock and poultry farming wastewater. To address this issue, firstly, the synthesis conditions of Fe/Mn nanoparticles (Fe/Mn NPs) were initially optimized using a response surface methodology (RSM) to yield highly active Fe/Mn NPs, where the application of RSM significantly increased the Fe/Mn NPs' efficiency in removing co-contamination OTC and Cu(II),respectively, from 45.8 to 86.2% and 14.9-67.2%. Secondly, scanning electron microscope and Nitrogen adsorption-desorption isotherms results showed that Fe/Mn NPs were composed of elliptic particles between 20 and 40 nm, a specific surface area of 59.5 m² g^-1, and a mean pore diameter of 5.27 nm. Fourier infrared spectrometer and X-ray photoelectron spectroscopy analysis revealed that amino, carboxyl and hydroxyl functional groups existed on the surface. Zeta potential indicated that Fe/Mn NPs maintained a high negative charge density between pH 1 and 11. These surface properties possessed by the green synthesized Fe/Mn NPs resulted in high adsorption efficiency for co-contamination OTC and Cu(II). Based on this, a removal mechanism based on a combination of complex-bridging effect, pore-filling, hydrogen bonding, surface complexation, ion exchange and electrostatic attraction was proposed. Finally, the assessment of Fe/Mn NPs used in swine wastewater demonstrated that both 99.9% OTC and 55.6% Cu(II) were removed.

Simultaneous removal of triclosan and Cd(Ⅱ) by bio-reduced graphene oxide and its mechanism

The co-existence of contaminants such as triclosan (TCS) and Cadmium in wastewater is a major public health problem because of their persistence and toxicity. In this study, bio-reduced graphene oxide (B-rGO) synthesized by Lysinibacillus sp. Simultaneously remove TCS and Cd(II), with adsorption capacities of 81.91 and 23.32 mg g^-1, for TCS and Cd (Ⅱ), respectively. This was significantly higher than that previously reported for commercially available reduced graphene oxide (C-rGO), which was only 31.94 and 2.01 mg g^-1, for TCS and Cd (Ⅱ), respectively. Fourier transform infrared spectroscopy (FTIR) showed that rGO surface-bound extracellular polymeric substances (EPS) played a key role in the observed enhanced contaminant removal, which was verified by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the absorption of both Cd(II) and TCS on B-rGO was confirmed by XPS and high-performance liquid chromatography (HPLC-UV). The adsorption kinetics of both TCS and Cd(II) fitted well to the pseudo-second-order model, while the adsorption isotherms of Cd(II) followed the Langmuir model, and triclosan the Freundlich model. A mechanism of simultaneous removal of TCS was proposed based on π-π interactions and hydrogen bonding, while Cd(II) was removed by a combination of electrostatic and chelation/complexation. Finally, the adsorption of TCS and Cd(II) by B-rGO in real wastewater was shown to be 76.67 and 16.53 mg g^-1, respectively, demonstrating that B-rGO has the potential for practical simultaneous removal of TCS and Cd(II) from wastewater.

Constructing Ni4/Fe@Fe3O4-g-C3N4 nanocomposites for highly efficient degradation of carbon tetrachloride from aqueous solution

Catalytic hydrodechlorination is one of the most potential remediation methods for chlorinated organic pollutants. In this study, Ni₄/Fe@Fe₃O₄-g-C₃N₄ (NFFOCN) nanocomposites were synthesized for carbon tetrachloride (CT) removal and characterized by SEM, XPS and FTIR. The characterization results demonstrated that the special functional groups of g-C₃N₄, especially NH groups, effectively alleviated the aggregation of nanoparticles. In addition, the C and N groups of g-C₃N₄ enhanced the catalytic dechlorination of CT by providing binding sites. The experimental results showed that NFFOCN could effectively remove CT over a wide initial pH range of 3-9, and the CT removal efficiency reached 94.7% after 35 min with only 0.15 g/L of NFFOCN at pH 5.5. The Cl^-, SO₄^2-, and HCO₃^- promoted the removal of CT, while HA and NO₃^- had the opposite effect. Furthermore, good sequential CT removal by NFFOCN nanocomposites was observed, and the CT removal efficiency reached 77.3% after four cycles. Based on the identification of products, a possible degradation pathway of CT was proposed. Moreover, the main mechanisms regarding CT removal included the direct reduction of nZVI (about 40.51%), adsorption (around 34.79%), and hydrodechlorination of CT by Ni⁰ using H₂ (about 19.40%).

High-capacity removal of oxytetracycline hydrochloride from wastewater via Mikania micrantha Kunth-derived biochar modified by Zn/Fe-layered double hydroxide

Antibiotic contamination in water has been an increasing global concern, and how to effectively remove antibiotics (e.g., oxytetracycline [OTC] hydrochloride) from wastewater becomes imperative. In this study, the biochar derived from an invasive plant (Mikania micrantha Kunth) was synthesized with Zn/Fe- layered double hydroxide (LDH) by co-precipitation method (ZnFe-LDH/MBC) to remove OTC from water. ZnFe-LDH/MBC posed the highest OTC removal performance of 426.61 mg/g. ZnFe-LDH/MBC exhibited stability and efficiency in OTC adsorption at different pH levels and under interfering conditions with co-existing ions, as well as outstanding regeneration capabilities during adsorption-desorption cycles. Furthermore, the removal of OTC by ZnFe-LDH/MBC was mediated by several processes including pore filling, hydrogen bonding force, electrostatic interaction, π-π interaction, as well as complexation. Consequently, ZnFe-LDH/MBC has excellent potential for the purification of OTC pollutants that is low-cost, efficient, and environmentally friendly.

Plant-Derived Iron Nanoparticles for Removal of Heavy Metals

Nanoparticle synthesis has seen exponential development recently as its characteristics of high surface area, high rate of adsorption, and easy, cost-effective synthesis have been exploited for the purpose of ground water purification via the removal of organic and inorganic compounds, along with the removal of heavy metals and microbes. The synthesis of Zero-Valent Iron Nanoparticles (ZVI NPs) by green methods has proved to be environmentally friendly in many ways as it employs the use of naturally occurring plant extracts. These nanoparticles have large surface areas and efficiently remove heavy metals. The reducing potential of these ZVI NPs is mostly −0.44 V, thus allowing them to reduce heavy metal compounds such as cadmium, lead, zinc, copper, and arsenic present in wastewater. Irradiated nanoparticles have also exhibited antimicrobial resistance and adsorption. It is also observed that nanoparticles show a higher rate of efficacy at a lower pH. The adsorbent, which is ZVI NPs in this case, when present in large doses reduces heavy metal compounds rapidly and effectively.

Cyclodextrin modified green synthesized graphene oxide@iron nanoparticle composites for enhanced removal of oxytetracycline

The presence of residual antibiotics will lead to potential environmental risks. Here cyclodextrins (CDs) were successfully used to modify graphene-based iron nanoparticles (GO@Fe NPs) to enhance the absorption of oxytetracycline hydrochloride (OTC). The removal of OTC decreased in the order: γCD-GO@Fe NPs > βCD-GO@Fe NPs > αCD-GO@Fe NPs > GO@Fe NPs, with better performance than that of bare GO and Fe NPs. Characterization techniques were applied to better understand how CDs impact the structure of GO@Fe NPs and improve removal performance. Raman and X-ray diffraction analysis showed that GO acted as a carrier to support Fe NPs within the grafted cyclodextrin, where GO also participated in the removal process. Cyclodextrin modified GO@Fe NPs had relatively small particle sizes (15 nm), with a high surface area (61.7 m² · g^-1). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy suggested that cyclodextrin acted as both a stabilizing and capping agent during green synthesis, which could protect the reactivity of Fe NPs and simultaneously reduce aggregation. A potential synthesis mechanism of cyclodextrins modified composites was also proposed, and subsequent wastewater testing indicated that γCD-GO@Fe NPs had high potential for practical applications.