One-pot hydrothermal synthesis of MXene Ti3C2/TiO2/BiOCl ternary heterojunctions with improved separation of photoactivated carries and photocatalytic behavior toward elimination of contaminants

Nanotechnology-assisted treatment of pharmaceuticals contaminated water

The presence of pharmaceutical compounds in wastewater due to an increase in industrialization and urbanization is a serious health concern. The demand for diverse types of pharmaceutical compounds is expected to grow as there is continuous improvement in the global human health standards. Discharge of domestic pharmaceutical personal care products and hospital waste has aggravated the burden on wastewater management. Further, the pharmaceutical water is toxic not only to the aquatic organism but also to terrestrial animals coming in contact directly or indirectly. The pharmaceutical wastes can be removed by adsorption and/or degradation approach. Nanoparticles (NPs), such as 2D layers materials, metal-organic frameworks (MOFs), and carbonaceous nanomaterials are proven to be more efficient for adsorption and/or degradation of pharmaceutical waste. In addition, inclusion of NPs to form various composites leads to improvement in the waste treatment efficacy to a greater extent. Overall, carbonaceous nanocomposites have advantage in the form of being produced from renewable resources and the nanocomposite material is biodegradable either completely or to a great extent. A comprehensive literature survey on the recent advancement of pharmaceutical wastewater is the focus of the present article.

Recent advancements in MXene-based nanocomposites as photocatalysts for hazardous pollutant degradation - A review

The recent expeditious industrialization and urbanization showcase the increasing need for renewable and non-renewable energy and the severe environmental crisis. In this regard, numerous 2-dimensional (2D) nanomaterials have been developed as a facile approach to meet the futuristic energy essentials and to resolve the crisis. In contrast, the newly explored 2D MXenes (transition metal carbide/nitrides/carbonitride) have been employed as an intriguing material for various environmental applications. This development is accredited to their unique properties, which include a vast surface area, strong electrical conductivity, fascinating photophysical properties, high mechanical properties, stability in an aqueous medium, high hydrophilicity, biocompatibility, ease of functionalization, and excellent thermal properties. MXenes act as a potential candidate in water desalination, energy storage devices such as electrodes of Li-ion batteries and pseudo capacitors, hydrogen production, sensors, and wastewater treatment. This review article deliberates the synthesis of MXene and nanocomposites of MXene and their photo-catalytic actions against various toxic pollutants such as organic dyes and heavy metals in wastewater. This review also precises the various preparation methods of MXene-based photocatalyst and the enhanced photocatalytic activity of MXene and MXene-based nanocomposites in wastewater treatment. Also, it details the attempts made to improve the photocatalytic activity of MXene-based nanocomposites in terms of their structural compositions. In addition, the merits and demerits of the MXene-based photocatalysts are deliberated, which may pave the way for future research in this arena.

Synthesis of AgBr/Ti3C2@TiO2 ternary composite for photocatalytic dehydrogenation of 1,4-dihydropyridine and photocatalytic degradation of tetracycline hydrochloride

In this work, AgBr/Ti₃C₂@TiO₂ ternary composite photocatalyst was prepared by a solvothermal and precipitation method with the aims of introducing Ti₃C₂ as a cocatalyst and TiO₂ as a compositing semiconductor. The crystal structure, morphology, elemental state, functional groups and photoelectrochemical properties were studied by XRD, SEM, TEM, XPS, FI-IR and EIS. The photocatalytic performances of the composites were investigated by the photodehydrogenation of diethyl 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate (1,4-DHP) and the photodegradation of tetracycline hydrochloride (TCH) under visible light irradiation (λ > 400 nm). The AgBr/Ti₃C₂@TiO₂ composite photocatalyst showed enhanced photocatalytic performance in both photocatalytic reactions. The photocatalytic activity of the composite photocatalyst is dependent on the proportional content of Ti₃C₂@TiO₂. With optimized Ti₃C₂@TiO₂ proportion, the photocatalytic ability of the AgBr/Ti₃C₂@TiO₂ composite was 24.5 times as high as that of Ti₃C₂@TiO₂ for photodehydrogenation of 1,4-DHP and 1.9 times as high as that of pure AgBr for photodegradation of TCH. The enhanced photocatalytic performance of the AgBr/Ti₃C₂@TiO₂ composite should be due to the formation of a p-n heterojunction structure between AgBr and Ti₃C₂@TiO₂ and the excellent electronic properties of Ti₃C₂, which enhanced the visible light absorption capacity, lowered the internal resistance, speeded up the charge transfer and reduced the recombination efficiency of photo-generated carriers. Mechanism studies showed that superoxide free radical (˙O₂^-) was the main active species. In addition, the composite photocatalyst also displayed good stability, indicating its reutilization in practical application.

Preparation of floating BiOCl0.6I0.4/ZnO photocatalyst and its inactivation of Microcystis aeruginosa under visible light

Frequent occurrence of harmful algal blooms has already threatened aquatic life and human health. In the present study, floating BiOCl_0.6I_0.4/ZnO photocatalyst was synthesized in situ by water bath method, and and applied in inactivation of Microcystis aeruginosa under visible light. The composition, morphology, chemical states, optical properties of the photocatalyst were also characterized. The results showed that BiOCl_0.6I_0.4 exhibited laminated nanosheet structure with regular shape, and the light response range of the composite BZ/EP-3 (BiOCl_0.6I_0.4/ZnO/EP-3) was tuned from 582 to 638 nm. The results of photocatalytic experiments indicated that BZ/EP-3 composite had stronger photocatalytic activity than a single BiOCl_0.6I_0.4 and ZnO, and the removal rate of chlorophyll a was 89.28% after 6 hr of photocatalytic reaction. The photosynthetic system was destroyed and cell membrane of algae ruptured under photocatalysis, resulting in the decrease of phycobiliprotein components and the release of a large number of ions (K⁺, Ca²⁺ and Mg²⁺). Furthermore, active species trapping experiment determined that holes (h⁺) and superoxide radicals (·O₂^-) were the main active substance for the inactivation of algae, and the p-n mechanism of photocatalyst was proposed. Overall, BZ/EP-3 showed excellent algal removal ability under visible light, providing fundamental theories for practical algae pollution control.

Rapid growth of MXene-based membranes for sustainable environmental pollution remediation

Water consumption has grown in recent years due to rising urbanization and industry. As a result, global water stocks are steadily depleting. As a result, it is critical to seek strategies for removing harmful elements from wastewater once it has been cleaned. In recent years, many studies have been conducted to develop new materials and innovative pathways for water purification and environmental remediation. Due to low energy consumption, low operating cost, and integrated facilities, membrane separation has gained significant attention as a potential technique for water treatment. In these directions, MXene which is the advanced 2D material has been explored and many applications were reported. However, research on MXene-based membranes is still in its early stages and reported applications are scatter. This review provides a broad overview of MXenes and their perspectives, including their synthesis, surface chemistry, interlayer tuning, membrane construction, and uses for water purification. Application of MXene based membrane for extracting pollutants such as heavy metals, organic contaminants, and radionuclides from the aqueous water bodies were briefly discussed. Furthermore, the performance of MXene-based separation membranes is compared to that of other nano-based membranes, and outcomes are very promising. In order to shed more light on the advancement of MXene-based membranes and their operational separation applications, significant advances in the fabrication of MXene-based membranes is also encapsulated. Finally, future prospects of MXene-based materials for diverse applications were discussed.

Two dimensional S-scheme Bi2WO6-TiO2-Ti3C2 nanocomposites for efficient degradation of organic pollutants under natural sunlight

Two-dimensional (2D) materials have fascinated the researchers to exploit their properties including large surface area, ability to act as a support and to form face-to-face interfacial contact with other 2D materials for fabricating efficient photocatalytic materials. In this work, Bi₂WO₆, TiO₂ and Ti₃C₂ nanosheets have been used synthesizing different series of binary Bi₂WO₆-TiO₂ and ternary Bi₂WO₆-TiO₂-Ti₃C₂ 2D nanocomposites by an electrostatic self-assembly synthesis route. The as-prepared pristine materials and binary and ternary nanocomposites were characterized by different structural, morphological and compositional characterization techniques to confirm their successful synthesis and 2D morphology. It was found that the optimized Bi₂WO₆-TiO₂ (20 wt%) and Bi₂WO₆-TiO₂ (20 wt%)-Ti₃C₂ (5 wt%) nanocomposites showed 97.0% and 98.5% degradation of methyl green in 80 min and 40 min, respectively, which was higher than their pristine counterparts. The enhanced activity was credited to the large surface area offered by 2D nanocomposites, pollutant adsorption and enhanced photogenerated charge separation and transfer facilitated by S-scheme mechanism and face-to-face interfacial contact of different components of these nanocomposites. This work delivers an example of highly efficient 2D nanocomposites and discusses the role of Ti₃C₂ as an electron acceptor in S-scheme photocatalytic system.

Heterostructured α-Bi2O3/BiOCl Nanosheet for Photocatalytic Applications

Photocatalytic degradation of organic pollutants in wastewater is recognized as a promising technology. However, photocatalyst Bi₂O₃ responds to visible light and suffers from low quantum yield. In this study, the α-Bi₂O₃ was synthetized and used for removing Cl^- in acidic solutions to transform BiOCl. A heterostructured α-Bi₂O₃/BiOCl nanosheet can be fabricated by coupling Bi₂O₃ (narrow band gap) with layered BiOCl (rapid photoelectron transmission). During the degradation of Rhodamine B (RhB), the Bi₂O₃/BiOCl composite material presented excellent photocatalytic activity. Under visible light irradiation for 60 min, the Bi₂O₃/BiOCl photocatalyst delivered a superior removal rate of 99.9%, which was much higher than pristine Bi₂O₃ (36.0%) and BiOCl (74.4%). Radical quenching experiments and electron spin resonance spectra further confirmed the dominant effect of electron holes h⁺ and superoxide radical anions ·O₂^- for the photodegradation process. This work develops a green strategy to synthesize a high-performance photocatalyst for organic dye degradation.

A Review on MXene Synthesis, Stability, and Photocatalytic Applications

Photocatalytic water splitting, CO₂ reduction, and pollutant degradation have emerged as promising strategies to remedy the existing environmental and energy crises. However, grafting of expensive and less abundant noble-metal cocatalysts on photocatalyst materials is a mandatory practice to achieve enhanced photocatalytic performance owing to the ability of the cocatalysts to extract electrons efficiently from the photocatalyst and enable rapid/enhanced catalytic reaction. Hence, developing highly efficient, inexpensive, and noble-metal-free cocatalysts composed of earth-abundant elements is considered as a noteworthy step toward considering photocatalysis as a more economical strategy. Recently, MXenes (two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides) have shown huge potential as alternatives for noble-metal cocatalysts. MXenes have several excellent properties, including atomically thin 2D morphology, metallic electrical conductivity, hydrophilic surface, and high specific surface area. In addition, they exhibit Gibbs free energy of intermediate H atom adsorption as close to zero and less than that of a commercial Pt-based cocatalyst, a Fermi level position above the H₂ generation potential, and an excellent ability to capture and activate CO₂ molecules. Therefore, there is a growing interest in MXene-based photocatalyst materials for various photocatalytic events. In this review, we focus on the recent advances in the synthesis of MXenes with 2D and 0D morphologies, the stability of MXenes, and MXene-based photocatalysts for H₂ evolution, CO₂ reduction, and pollutant degradation. The existing challenges and the possible future directions to enhance the photocatalytic performance of MXene-based photocatalysts are also discussed.

MXenes as emerging nanomaterials in water purification and environmental remediation

Environmental pollution has accelerated and intensified because of the acceleration of industrialization, therefore fabricating excellent materials to remove hazardous pollutants has become inevitable. MXenes as emerging transition metal nitrides, carbides or carbonitrides with high conductivity, hydrophilicity, excellent structural stability, and versatile surface chemistry, become ideal candidates for water purification and environmental remediation. Particularly, MXenes reveal excellent sorption capability and efficient reduction performance for various contaminants of wastewater. In this regard, a comprehensive understanding of the removal behaviors of MXene-based nanomaterials is necessary to explain how they remove various pollutants in water. The eliminate process of MXene-based nanomaterials is collectively influenced by the physicochemical properties of the materials themselves and the chemical properties of different contaminants. Therefore, in this review paper, the synthesis strategies and properties of MXene-based nanomaterials are briefly introduced. Then, the chemical properties, removal behaviors and interaction mechanisms of heavy metal ions, radionuclides, and organic pollutants by MXene-based nanomaterials are highlighted. The overview also emphasizes associated toxicity, secondary contamination, the challenges, and prospects of the MXene-based nanomaterials in the applications of water treatment. This review can supply valuable ideas for fabricating versatile MXene nanomaterials in eliminating water pollution.

MXene-based hybrid composites as photocatalyst for the mitigation of pharmaceuticals

Environmental contamination is a burning issue and has gained global attention in the present era. Pharmaceuticals are emerging contaminants affecting the natural environment worldwide owing to their extensive consumption particularly in developing countries where self-medication is a common practice. These pharmaceuticals or their degraded active metabolites enter water bodies via different channels and are continuous threat to the whole ecological system. There is a dire need to find efficient approaches for their removal from all environmental matrices. Photocatalysis is one of the most effective and simple approach, however, finding a suitable photocatalyst is a challenging task. Recently, MXenes (two-dimensional transition metal carbides/nitrides), a relatively new material has attracted increasing interest as photocatalysts due to their exceptional properties, such as large surface area, appreciable safety, huge interlayer spacing, thermal conductivity, and environmental flexibility. This review describes the recent advancements of MXene-based composites and their photocatalytic potential for the elimination of pharmaceuticals. Furthermore, present limitations and future research requirements are recommended to attain more benefits of MXene-based composites for the purification of wastewater.

MXenes based nano-heterojunctions and composites for advanced photocatalytic environmental detoxification and energy conversion: A review

Extensive research is being done to develop multifunctional advanced new materials for high performance photocatalytic applications in the field of energy production and environmental detoxification, MXenes have emerged as promising materials for enhancing photocatalytic performance owing to their excellent mechanical properties, appropriate Fermi levels, and adjustability of chemical composition. Numerous experimental and theoretical research works implied that the dimensions of MXenes have a significant impact on their performance. For photocatalysis to thrive in the future, we must understand the current state of the art for MXene in different dimensions. Using MXene co-catalysts in widely used in photocatalytic applications such as CO₂ reduction, hydrogen production and organic pollutant oxidation, this study focuses on the most recent developments in MXenes based materials, structural modifications, innovations in reaction and material engineering. It has been reported that using 5 mg of CdS-MoS₂-MXene researchers were able to generate as high as 9679 μmol/g/h hydrogen under visible light. The MXenes based heterojunction photocatalyst Co₃O₄/MXene was utilized to degrade 95% bisphenol A micro-pollutant in just 7 min. Numerous novel materials, their preparations and performances have been discussed. Depending upon the nature of MXene-based materials, the synthesis techniques and photocatalytic mechanism of MXenes as co-catalyst are also summarized. Finally, some final thoughts and prospects for developing highly efficient MXene-based photocatalysts are provided which will indeed motivate researchers to design novel hybrid materials based on MXenes for sustainable solutions to energy and pollution issues.

One-Step Microwave-Assisted Synthesis and Visible-Light Photocatalytic Activity Enhancement of BiOBr/RGO Nanocomposites for Degradation of Methylene Blue

In this study, bismuth oxybromide/reduced graphene oxide (BiOBr/RGO), i.e. BiOBr-G nanocomposites, were synthesized using a one-step microwave-assisted method. The structure of the synthesized nanocomposites was characterized using Raman spectroscopy, X-ray diffractometry (XRD), photoluminescence (PL) emission spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible diffuse reflection spectroscopy (DRS). In addition, the ability of the nanocomposite to degrade methylene blue (MB) under visible light irradiation was investigated. The synthesized nanocomposite achieved an MB degradation rate of above 96% within 75 min of continuous visible light irradiation. In addition, the synthesized BiOBr-G nanocomposite exhibited significantly enhanced photocatalytic activity for the degradation of MB. Furthermore, the results revealed that the separation of the photogenerated electron-hole pairs in the BiOBr-G nanocomposite enhanced the ability of the nanocomposite to absorb visible light, thus improving the photocatalytic properties of the nanocomposites. Lastly, the MB photo-degradation mechanism of BiOBr-G was investigated, and the results revealed that the BiOBr-G nanocomposites exhibited good photocatalytic activity.

Construction of Bi2O2CO3/Ti3C2 heterojunctions for enhancing the visible-light photocatalytic activity of tetracycline degradation

Bi₂O₂CO₃ (BOC) was successfully loaded on a highly conductive Ti₃C₂ surface by the hydrothermal method, forming a unique BOC/Ti₃C₂ heterostructure. The use of advanced characterization methods reveals the composition, morphology and photoelectric properties of the material. The results show that the interface formed by close contact between BOC and Ti₃C₂ provides an effective channel for charge transfer between the two. Importantly, the photocatalytic degradation efficiency of BOC/Ti₃C₂ for tetracycline (TC) is ~80%, which is significantly higher than the degradation efficiency of pure BOC and pure Ti₃C₂ for TC. In addition, BOC/Ti₃C₂ still has high catalytic activity in the degradation of complex mixed antibiotics. This is because BOC and Ti₃C₂ have large specific surface areas, high light absorption capacity and efficient carrier separation after recombination. At the same time, the detected superoxide radicals (O^2-) and holes (h⁺) are the main active substances. The degradation pathway and catalytic mechanism of the photocatalytic degradation of TC by BOC/Ti₃C₂ are further explained. This research designed and developed a BOC/Ti₃C₂ composite material for the photocatalytic degradation of tetracycline and mixed antibiotic wastewater, providing experimental methods and ideas for actual wastewater treatment.