Two-dimensional MXenes: recent emerging applications

MXenes, are a rapidly growing family of two-dimensional materials exhibiting outstanding electronic, optical, mechanical, and thermal properties with versatile transition metal and surface chemistries. A wide range of transition metals and surface termination groups facilitate the properties of MXenes to be easily tuneable. Due to the physically strong and environmentally stable nature of MXenes, they have already had a strong presence in different fields, for instance energy storage, electrocatalysis, water purification, and chemical sensing. Some of the newly discovered applications of MXenes showed very promising results, however, they have not been covered in any review article. Therefore, in this review we comprehensively review the recent advancements of MXenes in various potential fields including energy conversion and storage, wearable flexible electronic devices, chemical detection, and biomedical engineering. We have also presented some of the most exciting prospects by combining MXenes with other materials and forming mixed dimensional high performance heterostructures based novel electronic devices.

Six CoII coordination polymers exhibiting UV-light-driven photocatalysis for the degradation of organic dyes

Six different Co^II coordination polymers based on a new bis-pyridyl-bis-amide and polycarboxylates were obtained, showing photocatalytic activity for organic dyes.

Silver embellished PANI/CNT nanocomposite for antimicrobial activity and sequestration of dye based on RSM modelling

Silver doped PANI/CNT (Ag-PANI/CNT) nanocomposite was synthesized and investigated as adsorbent for its possible application in the elimination of organic dye Brilliant Blue G (BBG). The morphological characteristics of Ag-PANI/CNT were studied using Fourier transform infrared, scanning electron microscopy, elemental mapping, transmission electron microscopy and X-ray diffraction. The response of operational parameters given as adsorbent dosage, concentration, pH and contact time for dye removal were investigated by using Response Surface Methodology (RSM). The results from RSM suggested that the efficiency of BBG elimination is 98.7 under the optimum conditions of experimental factors. The adsorption studies showed that the equilibrium data fitted well with Langmuir isotherm model compared to Freundlich. Finally, the antimicrobial activities of Ag-PANI/CNT were tested against bacterial strain Escherichia coli and Salmonella typhi and fungal strains Aspergillus niger.

ZnCl2-activated carbon from soybean dregs as a high efficiency adsorbent for cationic dye removal: isotherm, kinetic, and thermodynamic studies

Activated carbon was prepared from soybean dregs using chemical activation by zinc chloride. The influence of activation parameters such as impregnation ratio, activation temperature and carbonization time was investigated. The physicochemical properties of activated carbon were characterized using SEM, FTIR, BET and TGA, respectively. The effect factors including pH, contact time, temperature and dose on the adsorption properties of methylene blue onto activated carbon were studied. The adsorption equilibrium data of methylene blue onto activated carbon were well fitted to the Langmuir model, giving a maximum adsorption capacity of 255.10 mg/g. It indicates that activated carbon is a promising adsorbent for removing methylene blue from aqueous solution. The kinetic data were well described by the pseudo-second-order model. Thermodynamic parameters indicate that adsorption process is spontaneous and endothermic.The effect of temperature on MB adsorbed by AC shows that the equilibrium adsorption capacity increases with increasing temperature from 303 to 323 K. Increasing adsorption capacities with temperature indicate that the adsorption of MB onto AC is controlled by an endothermic reaction.

Electrostatically controlled plasmonic effects of gold nanoparticles with indigo-carmine functionation for rapid and straightforward colorimetric detection of Cu2+ ions

A colorimetric sensor is fabricated for effective on-site monitoring of Cu²⁺ ions content based on the distance-dependent optical properties of gold nanoparticles-polyvinyl alcohol-citrate (Au-NPs-PVA-Cy) which plasmonic effect electrostatically was controlled by PVA-Cy stabilizing indigo-carmine (IC) functionalizing. The surface-modified gold nanoparticles were extremely stable with a strong affinity toward Cu²⁺ ions. Citrate ion was employed as a cross-linking agent for pairs of Au-NPs-PVA-Cy and IC for stabilizing coordination between Cu²⁺ ion and IC. The active materials were characterized by UV-Vis, SEM, DLS, XRD, FT-IR, and EDS analyses. The sensor response toward Cu²⁺ ion was found to be linear in the range of 0.0974 to 3.27 μM with the limit of detection and quantification values of 0.021 and 0.07 μM, respectively. The sensor represents good sensitivity and stability, promisingly suggesting this device for the accurate and repeatable determination of Cu²⁺ in real water samples. The effect of different foreign ions on the selectivity of the sensor was checked. The sensor has a long shelf life in comparison to other similar colorimetric sensors. Also, it shows a repeatable response with RSD% of 2.02%. Thus, the sensing of Cu²⁺ ions based on the electrostatically control plasmonic of Au-NPs-PVA-Cy was developed with proper signaling based on the color change from dark blue to light blue as readily seen by the naked eye. Furthermore, the efficient environmental applicability of this simple and rapid determination of the Cu²⁺ sensor is proved.

Colorimetric determination of F-, Br- and I- ions by Ehrlich's bio-reagent oxidation over enzyme mimic like gold nanoparticles: Peroxidase-like activity and multivariate optimization

Citrate and polyvinyl alcohol capped gold nanoparticles (PVA-GNPs) were synthesized via chemical reduction technique and fully characterized by DLS, SEM, EDS, XRD, UV-Vis and FT-IR analysis. A simple and practical colorimetric sensor based on red-ox reaction of p-dimethylaminobenzaldehyde (DABA) as ehrlich's bio-reagent and Au(III) with H₂O₂ on PVA-GNPs mimic catalyst with enzyme-like activity, has been fabricated for determination of F^-, Br^- and I^- halide anions. Prepared PVA-GNPs, can simultaneously catalyze the disintegration of H₂O₂, that used to reduce Au(III) ions into co-doped Au-NPs and oxidation of p-dimethylaminobenzaldehyde ehrlich's bio-reagent while in the presence of halide ions Au-X complex can be formed and improved sensor selectivity. Halide ions (F^-, Br^- and I^-) effectively diminishes the catalytic activity of GNPs to disintegrate oxygenated water by the interaction among Au⁺ and Au⁰ and suppressing oxidation of p-dimethylaminobenzaldehyde ehrlich's bio-reagent. In this system which contains PVA-GNPs, H₂O₂, p-dimethylaminobenzaldehyde ehrlich's bio-reagent, and Au(III), increasing the halide ions (F^-, Br^- and I^-) concentration show color changes from deep green to red. In view of this rule, in this work, a novel colorimetric technique for sensitive determination of F^-, Br^- and I^- was developed. This method has the detection limits of 2.60 × 10^-6 M, 6.64 × 10^-8 M and 9.93 × 10^-9 M and linear ranges between 1.98 × 10^-5-1.22 × 10^-3 M, 1.99 × 10^-6-2.0 × 10^-4 M and 1.07 × 10^-7- 2.86 × 10^-5 M for F^-, Br^- and I^-, respectively. Assays are highly selective over other ions. They effectively applied to detection of halide ions in real water samples.

Developing a new colorimetric bioassay for iodide determination based on gold supported iridium peroxidase catalysts

A schematic sketch of the colorimetric bioassay for iodide determination based on gold supported iridium peroxidase catalysts.

Sonochemical synthesis and characterization of four nanostructural nickel coordination polymers and photocatalytic degradation of methylene blue

Four nanostructural nickel(II) coordination polymers {[Ni(ttpa)(1,4-ndc)(H₂O)₂]·2H₂O}_n (1), {[Ni(ttpa)(1,3-bda)]·2H₂O·DMF}_n (2·2H₂O·DMF), {[Ni(ttpa)(1,4-bdc)]·H₂O}_n (3) and {[Ni(ttpa)(aip)(H₂O)]·3H₂O}_n (4·3H₂O) were synthesized using hydrothermal and sonochemical methods (ttpa = tris(4-(1,2,4-triazol-1-yl)phenyl)amine, 1,4-ndc = 1,4-naphthalenedicarboxylate, 1,3-bda = 1,3-benzenediacetate, 1,4-bdc = 1,4-benzenedicarboxylate, aip = 5-aminoisophthalate), and characterized by elemental analysis, IR spectra, scanning electron microscopy, single-crystal and powder X-ray diffraction analysis, optical band gaps, VB XPS spectra and luminescence. The effects of sonication power, time and frequency on the size and morphology of nano-sized 1-4 have been studied. 1 exhibits an unusual 2D + 2D → 3D inclined polycatenated motif based on the (3,3)-coordinated 6³-hcb topology. 2 shows a (3,4)-coordinated 2D network of the bey topology. 3 presents a rare example of the 4-fold interpenetrating array of (3,5)-coordinated 3D network belonging to the 35T1 topology type. 4 displays an unusual 2D → 3D polythreaded network based on 2D sql networks. 1-4 exhibit luminescent emissions at 409, 399, 413 and 402 nm, respectively. 1-4 are semiconducting in nature, with E_g of 2.12 eV (1), 2.34 eV (2), 2.32 eV (3), and 2.47 eV (4). 1-4 are good catalysts for the degradation of MB under visible light irradiation. The effects of the size and morphology of nano-sized 1-4 on the photocatalytic efficiencies were studied. The higher sonication frequency obtains uniform and smaller nano-sized coordination polymers which have higher catalytic efficiencies.

Bi2WO6/Ag3PO4–Ag Z-scheme heterojunction as a new plasmonic visible-light-driven photocatalyst: performance evaluation and mechanism study

The Bi₂WO₆/Ag₃PO₄–Ag Z-scheme heterojunction, as a novel plasmonic visible-light-driven photocatalyst, was prepared by ultrasound assisted in situ precipitation and the hydrothermal method and was further characterized using multiple techniques.

A Bi2WO6/Ag2S/ZnS Z-scheme heterojunction photocatalyst with enhanced visible-light photoactivity towards the degradation of multiple dye pollutants

A novel visible-light-driven Z-scheme heterojunction, Bi₂WO₆/Ag₂S/ZnS, was synthesized and its photocatalytic activity was evaluated for the treatment of a binary mixture of dyes, and its physicochemical properties were characterized using FT-IR, XRD, DRS and FE-SEM techniques. The Bi₂WO₆/Ag₂S/ZnS Z-scheme heterojunctions not only facilitate the charge separation and transfer, but also maintain the redox ability of their components. The superior photocatalytic activity demonstrated by the Z-scheme Bi₂WO₆/Ag₂S/ZnS attributes its unique properties such as the rapid generation of electron–hole pairs, slow recombination rate, and narrow bandgap. The performance of the Bi₂WO₆/Ag₂S/ZnS was evaluated for the simultaneous degradation of methyl green (MG) and auramine-O (AO) dyes, while the influences of the initial MG concentration (4–12 mg L⁻¹), initial AO concentration (2–6 mg L⁻¹), pH (3–9), irradiation time (60–120 min) and photocatalyst dosage (0.008–0.016 g L⁻¹) were investigated through the response surface methodology. The desirability function approach was applied to optimize the process and results revealed that maximum photocatalytic degradation efficiency was obtained at optimum conditions including 6.08 mg L⁻¹ of initial MG concentration, 4.04 mg L⁻¹ of initial AO concentration, 7.25 of pH, 90.58 min of irradiation time and 0.013 g L⁻¹ of photocatalyst dosage. In addition, a possible photocatalytic mechanism of the Bi₂WO₆/Ag₂S/ZnS heterojunction was proposed based on the photoinduced charge carriers.

A Z-scheme Bi₂WO₆/Ag₂S/ZnS heterojunction was successfully synthesized as a novel visible-light-driven photocatalyst for the degradation of multiple dye pollutants.

Applications of 2D MXenes in energy conversion and storage systems

This article provides a comprehensive review of MXene materials and their energy-related applications.

A simple approach for the sonochemical loading of Au, Ag and Pd nanoparticle on functionalized MWCNT and subsequent dispersion studies for removal of organic dyes: Artificial neural network and response surface methodology studies

In this study, the artificial neural network (ANN) and response surface methodology (RSM) based on central composite design (CCD) were applied for modeling and optimization of the simultaneous ultrasound-assisted removal of quinoline yellow (QY) and eosin B (EB). The MWCNT-NH₂ and its composites were prepared by sonochemistry method and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis's. Initial dyes concentrations, adsorbent mass, sonication time and pH contribution on QY and EB removal percentage were investigated by CCD and replication of experiments at conditions suggested by model has results which statistically are close to experimented data. The ultrasound irradiation is associated with raising mass transfer of process so that small amount of the adsorbent (0.025 g) is able to remove high percentage (88.00% and 91.00%) of QY and EB, respectively in short time (6.0 min) at pH = 6. Analysis of experimental data by conventional models is good indication of Langmuir efficiency for fitting and explanation of experimented data. The ANN based on the Levenberg-Marquardt algorithm (LMA) combined of linear transfer function at output layer and tangent sigmoid transfer function at hidden layer with 20 hidden neurons supply best operation conditions for good prediction of adsorption data. Accurate and efficient artificial neural network was obtained by changing the number of neurons in the hidden layer, while data was divided into training, test and validation sets which contained 70, 15 and 15% of data points respectively. The Average absolute deviation (AAD)% of a collection of 128 data points for MWCNT-NH₂ and composites is 0.58%.for EB and 0.55 for YQ.

Sonochemical synthesis of amide-functionalized metal-organic framework/graphene oxide nanocomposite for the adsorption of methylene blue from aqueous solution

Graphene oxide-[Zn₂(oba)₂(bpfb)]·(DMF)₅ metal-organic framework nanocomposite (GO-TMU-23; H₂oba=4,4'-oxybisbenzoic acid, bpfb=N,N'-bis-(4-pyridylformamide)-1,4-benzenediamine, DMF=N,N-dimethylformamide) is prepared through a simple and large-scale sonochemical preparation method at room temperature. The obtained nanocomposite is characterized by Field Emission Scanning Electron Microscopy (FE-SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Additionally, the absorption ability of GO-TMU-23 nanocomposite toward cationic dye methylene blue was also performed. Significantly, GO-TMU-23 nanocomposite exhibits remarkably accelerated adsorption kinetics for methylene blue in comparison with the parent materials. The adsorption process shows that 90% of the dye has been removed and the equilibrium status has been reached in 2min by using the nanocomposites as the adsorbent.

Sonochemical-assisted synthesis of CuO/Cu2O/Cu nanoparticles as efficient photocatalyst for simultaneous degradation of pollutant dyes in rotating packed bed reactor: LED illumination and central composite design optimization

CuO/CuO₂/Cu nanoparticles were prepared by sonochemical combined thermal synthesis method and used as new photocatalyst for simultaneous photocatalytic degradation of safranin O (SO) and methylene blue (MB) dyes in rotating packed bed reactor equipped to blue light emitting diode (LED). The physicochemical properties of the synthesized CuO/Cu₂O/Cu nanoparticles were investigated by XRD, SEM and DRS analysis. The band-gap of the prepared CuO/Cu₂O/Cu-NPs was estimated to be about 1.42eV which is appropriate for photodegradation process under blue light irradiation. In rotating packed bed reactors, two key parameters are very important, one high centrifugal field and other porous media, which intensify mass transfer operation leads to photodegradation improvement. The maximum photodegradation efficiency was obtained at pH of 6 and subsequently the effects of CuO/Cu₂O/Cu-NPs dosage, rotational speed, initial dyes concentration, flow rate and reaction time were studied by central composite design (CCD) and optimized values were found to be 0.3g/L, 900rpm, 10mg/L of both dyes, 0.3L/min and 90min, respectively. Finally, results showed that synergistic effects induced by forming Cu₂O/CuO heterojunction containing Cu-NPs co-cocatalyst greatly accelerate electron transfer and effectively retard the reduction of CuO by photo-generated electrons.

Novel visible light-driven Cu-based MOFs/Ag2O composite photocatalysts with enhanced photocatalytic activity toward the degradation of orange G: their photocatalytic mechanism and optimization study

The present work is devoted to the synthesis of two visible light-driven Cu-based metal organic frameworks composited with Ag₂O nanoparticles.

Adsorption and biodegradation of dye in wastewater with Fe3O4@MIL-100 (Fe) core-shell bio-nanocomposites

Adsorption and improved biodegradation of dyes in wastewater was achieved with Fe₃O₄@MIL-100 core-shell bio-nanocomposites, which were prepared by a step-by-step strategy and attached to the surface of bacteria via zero-length carbodiimide chemistry. The Fe₃O₄@MIL-100 (Fe) nano-composite showed excellent dye adsorption properties and the overall dye removal process followed second-order kinetics. The dye AO10 was completely eliminated from solution by the combined effects of adsorption and biodegradation within 15 and 25 h from initial dye concentrations of 25 and 50 mg/L, respectively. The time to degrade the dye decreased from 11 h for the free microorganisms to 5 h for the bio-nanocomposite. The procedure was non-toxic, allowed for magnetic separation of the bio-nanocomposite from solution, and showed good cycling performance for the removal of dye. Hence, the strategy of surface-engineering bacteria shows great potential for the treatment of dyes from industrial effluents.

Fabrication, characterization and photoelectrochemical activity of tungsten-copper co-sensitized TiO2 nanotube composite photoanodes

Tungsten-copper co-sensitized TiO₂ nanotube films on titanium substrate, used as photoanodes in photoelectrochemical (PEC) water splitting to produce hydrogen, have been synthesized via anodization and chemical bath deposition (CBD) methods. Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were used to study the morphology and elemental composition of the synthetic samples. UV-Vis diffuse reflection spectroscopy (UV-Vis DRS) was sued to investigate the optical features of the samples. The impact of copper and tungsten ratio on the photocatalytic behavior of co-sensitized TiO₂ nanotube photoelectrodes in PEC water splitting has been investigated. High photocatalytic activity has been exhibited by the co-sensitized TiO₂ nanotube samples due to the synergistic effects of the copper and tungsten. Sample T4 had the highest photoelectrochemical activity compared with other samples. In addition, this sample exhibited outstanding photochemical stability even after four runs in the photocatalytic test. A simple method for the synthesis of high performance co-sensitized TiO₂ nanotube photocatalysts for application in solar energy conversion has thus been proposed in this work. The advantages of these new photoanodes for practical applications are low cost, ease of synthesis, high activity in visible light and excellent stability.

Surface modification of TiO2 particles with the sono-assisted exfoliation method

This study reported a novel approach to optimize the photocatalytic property of anatase TiO₂ particles by delaminating their outer surface into highly reactive nanosheets via the sono-assisted exfoliation method. To modify the surface, TiO₂ particles were dispersed in aqueous solution of 10M sodium hydroxide (NaOH) and tetrabutylammonium hydroxide (TBAOH), followed by irradiation with high intensity ultrasonic wave (20kHz, 150W/cm²) for 60min. The intercalation and exfoliation processes were accelerated with the driving force of the extreme acoustic cavitation leading to the delamination of TiO₂ nanosheets with highly reactive exposed {001} facets from the mother TiO₂ crystals. The presence of TBAOH increased yield of nanosheets formation and stabilized the nanosheet structure. The unique morphology of the surface modified TiO₂ particles provided benefits in increasing the specific surface area and lowering the optical band gap energy (E_g) and electron-hole recombination rate resulting in an enhancement of methylene blue dye degradation efficiency. The surface modification of TiO₂ particles by the sono-assisted exfoliation method can optimize the photocatalytic activity by yielding synergetic effects of the high surface reactive sites of the nanosheets and the high degree of crystallinity of the bulk structure.

Ultrasonic-assistant fabrication of cocoon-like Ag/AgFeO2 nanocatalyst with excellent plasmon enhanced visible-light photocatalytic activity

The AgFeO₂ delafossite was reported as a potential photocatalyst as well as its intense recombination rate of photogeneration charge carriers. In this work, we utilized plasmon modification method to enhance the photocatalytic activity of AgFeO₂. Silkworm cocoon like Ag/AgFeO₂ nanocatalyst was synthesized by an ultrasonic enhanced reduction method. XRD, HRTEM and XPS results demonstrated the well dispersed Ag⁰ on the surface of AgFeO₂. Under visible light irradiation, 20mg/L of ARG solution was completely degraded by 0.25g/L of Ag/AgFeO₂ photocatalyst with pseudo-first-order rate of 0.040min^-1. The inducement of the prominently enhanced photocatalytic activity of Ag/AgFeO₂ was deeply analyzed. Significant decreased intensity of photoluminescence (PL) spectra suggested the superior separation of photo-induced electrons and holes of Ag/AgFeO₂ as compared to that of AgFeO₂. The free h⁺ was confirmed as the dominant active species for the pollutant degradation. Ultimately, the photodegradation mechanism was proposed and discussed.

Ultrasonic-assisted magnetic solid phase extraction of morphine in urine samples by new imprinted polymer-supported on MWCNT-Fe3O4-NPs: Central composite design optimization

Multiwalled carbon nanotubes (MWCNTs) were magnetized with Fe3O4 nanoparticles (MWCNTs-Fe3O4-NPs) and subsequently coated by vinyl end groups (Vinyltrimethoxysilane). MWCNT-Fe3O4-NPs were used as support for a new morphine (MO) molecularly imprinted polymer (MWCNT-Fe3O4-NPs@MO-MIP) by surface imprinting polymerization method. The MWCNT-Fe3O4-NPs@MO-MIP was characterized by FTIR, VSM and SEM techniques and successfully used for determination of MO. Ultrasonic-assisted magnetic solid phase extraction followed by UV-vis spectrophotometer (UAMSPE-UV-vis) was investigated for MWCNT-Fe3O4-NPs@MO-MIP and compared with non-imprinted polymer (NIP) using batch method. Central composite design under response surface methodology was used for the evaluation of the effect of variables, individually, as well as their possible interaction effects on the adsorption process. The variables such as sonication time, MWCNT-Fe3O4-NPs@MO-MIP mass, initial concentration of MO and pH were investigated in this study. At optimum experimental conditions, UAMSPE-UV-vis method was exhibited a linear range of 0.8-8.7mgL(-1) of the MO concentration with a detection limit of 0.18mgL(-1). The relative standard deviation for the analyte was found to be lower than 2.32%. The MWCNT-Fe3O4-NPs@MO-MIP adsorption capacity was found to be 37.01mgg(-1). The enrichment and preconcentration factors were found to be 107.01 and 98.21, respectively. The developed method was finally applied successfully to the determination of MO in urine and wastewater samples with the recoveries ranged from 96.40 to 105.6%.

HKUST-1-MOF–BiVO4 hybrid as a new sonophotocatalyst for simultaneous degradation of disulfine blue and rose bengal dyes: optimization and statistical modelling

A new hybrid material composed of BiVO₄ and HKUST-1 MOF (HKUST-1-MOF–BiVO₄), which is active under blue light irradiation, was synthesized and characterized by XRD, FE-SEM, BET, BJH, EDS and DRS analysis.

BiPO4/Bi2S3-HKUST-1-MOF as a novel blue light-driven photocatalyst for simultaneous degradation of toluidine blue and auramine-O dyes in a new rotating packed bed reactor: optimization and comparison to a conventional reactor

BiPO₄/Bi₂S₃-HKUST-1-MOF as a novel blue light active photocatalyst was synthesized and characterized by X-ray XRD, SEM, PL, BET, BJH and DRS.