Enhanced visible light photocatalysis by TiO2-BN enabled electrospinning of nanofibers for pharmaceutical degradation and wastewater treatment

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.

Preparation and modification methods of defective titanium dioxide-based nanoparticles for photocatalytic wastewater treatment-a comprehensive review

The rapid population growth and industrial expansion worldwide have created serious water contamination concerns. To curb the pollution issue, it has become imperative to use a versatile material for the treatment. Titanium dioxide (TiO₂) has been recognized as the most-studied nanoparticle in various fields of science and engineering due to its availability, low cost, efficiency, and other fascinating properties with a wide range of applications in modern technology. Recent studies revealed the photocatalytic activity of the material for the treatment of industrial effluents to promote environmental sustainability. With the wide band gap energy of 3.2 eV, TiO₂ can be activated under UV light; thus, many strategies have been proposed to extend its photoabsorption to the visible light region. In what follows, this has generated increasing attention to study its characteristics and structural modifications in different forms for photocatalytic applications. The present review provides an insight into the understanding of the synthesis methods of TiO₂, the current progress in the treatment techniques for the degradation of wide environmental pollutants employing modified TiO₂ nanoparticles, and the factors affecting its photocatalytic activities. Further, recent developments in using titania for practical applications, the approach for designing novel nanomaterials, and the prospects and opportunities in this exciting area have been discussed.

Tunable TiO2-BN-Pd nanofibers by combining electrospinning and atomic layer deposition to enhance photodegradation of acetaminophen

The demand for fresh and clean water sources is increasing globally, and there is a need to develop novel routes to eliminate micropollutants and other harmful species from water. Photocatalysis is a promising alternative green technology that has shown great performance in the degradation of persistent pollutants. Titanium dioxide is the most used catalyst owing to its attractive physico-chemical properties, but this semiconductor presents limitations in the photocatalysis process due to the high band gap and the fast recombination of the photogenerated carriers. Herein, a novel photocatalyst has been developed, based on titanium dioxide nanofibers (TiO₂ NFs) synthesized by electrospinning. The TiO₂ NFs were coated by atomic layer deposition (ALD) to grow boron nitride (BN) and palladium (Pd) on their surface. The UV-Vis spectroscopy measurements confirmed the increase of the band gap and the extension of the spectral response to the visible range. The obtained TiO₂/BN/Pd nanofibers were then tested for photocatalysis, and showed a drastic increase of acetaminophen (ACT) degradation (>90%), compared to only 20% degradation obtained with pure TiO₂ after 4 h of visible light irradiation. The high photocatalytic activity was attributed to the good dispersion of Pd NPs on TiO₂-BN nanofibers, leading to a higher transfer of photoexcited hole carriers and a decrease of photogenerated electron-charge recombination. To confirm its reusability, recycling tests on the hybrid photocatalyst TiO₂/BN/Pd have been performed, showing a good stability over 5 cycles under UV and visible light. In addition, toxicity tests as well as quenching tests were carried out to check the toxicity of the byproducts formed and to determine active species responsible for the degradation. The results presented in this work demonstrate the potential of TiO₂/BN/Pd nanomaterials, and open new prospects for the preparation of tunable photocatalysts.

A comprehensive review on preparation, functionalization and recent applications of nanofiber membranes in wastewater treatment

The direct discharge of significant amounts of polluted water into water bodies causes adverse ecological and human health effects. This severe deterioration in water quality creates significant challenges to meet the growing demand for clean water. Therefore, the world urgently needs environmentally friendly advanced technology to overcome this global crisis. In this regard, nanofiber-based membrane filtration is a promising technique in wastewater remediation because of their huge surface area, extremely porous structure, amenable pore size/pore size distribution, variety of material choices, and flexibility to modification with other functional materials. However, despite their unique properties, fouling, poor mechanical properties, shrinkage, and deformation are major drawbacks of nanofiber membranes for treating wastewater. This review presents a comprehensive overview of nanofiber membranes' fabrication and function in water purification applications as well as providing novel approaches to overcoming/alleviating the mentioned disadvantages. The review first presents nanofiber membrane preparation methods, focusing on electrospinning as a versatile and viable technique alongside discussing the parameters controlling nanofiber morphology. Afterward, the functionalization of nanofiber membranes by combining them with other nanomaterials, such as metal and metal-oxide nanoparticles, carbon nanotubes, metal-organic frameworks, and biomolecules, were demonstrated and discussed. In addition, nanofiber membranes functionalized with microorganisms were highlighted. Finally, we introduced and discussed in detail the most relevant and recent advances in nanofiber applications in wastewater treatment in the context of removing different pollutants (e.g., heavy metals, nutrients, radioactive elements, pharmaceuticals, and personal care products, dyes, and pesticides). Moreover, the promising antimicrobial ability of nanofiber membranes in removing microorganisms from wastewater has been fully underscored. We believe this comprehensive review could provide researchers with preliminary data and guide both researchers and producers engaged in the nanofiber membrane industry, letting them focus on the research gaps in wastewater treatment.

Two-Dimensional Nanomaterials for the Removal of Pharmaceuticals from Wastewater: A Critical Review

The removal of pharmaceuticals from wastewater is critical due to their considerable risk on ecosystems and human health. Additionally, they are resistant to conventional chemical and biological remediation methods. Two-dimensional nanomaterials are a promising approach to face this challenge due to their combination of high surface areas, high electrical conductivities, and partially optical transparency. This review discusses the state-of-the-art concerning their use as adsorbents, oxidation catalysts or photocatalysts, and electrochemical catalysts for water treatment purposes. The bibliographic search bases upon academic databases including articles published until August 2021. Regarding adsorption, high removal capacities (>200 mg g−1) and short equilibrium times (<30 min) are reported for molybdenum disulfide, metal-organic frameworks, MXenes, and graphene oxide/magnetite nanocomposites, attributed to a strong adsorbate-adsorbent chemical interaction. Concerning photocatalysis, MXenes and carbon nitride heterostructures show enhanced charge carriers separation, favoring the generation of reactive oxygen species to degrade most pharmaceuticals. Peroxymonosulfate activation via pure or photo-assisted catalytic oxidation is promising to completely degrade many compounds in less than 30 min. Future work should be focused on the exploration of greener synthesis methods, regeneration, and recycling at the end-of-life of two-dimensional materials towards their successful large-scale production and application.

Enhanced catalytic ozonation of ibuprofen using a 3D structured catalyst with MnO2 nanosheets on carbon microfibers

Heterogeneous catalytic ozonation is an effective approach to degrade refractory organic pollutants in water. However, ozonation catalysts with combined merits of high activity, good reusability and low cost for practical industrial applications are still rare. This study aims to develop an efficient, stable and economic ozonation catalyst for the degradation of Ibuprofen, a pharmaceutical compound frequently detected as a refractory pollutant in treated wastewaters. The novel three-dimensional network-structured catalyst, comprising of δ-MnO₂ nanosheets grown on woven carbon microfibers (MnO₂ nanosheets/carbon microfiber), was synthesized via a facile hydrothermal approach. Catalytic ozonation performance of Ibuprofen removal in water using the new catalyst proves a significant enhancement, where Ibuprofen removal efficiency of close to 90% was achieved with a catalyst loading of 1% (w/v). In contrast, conventional ozonation was only able to achieve 65% removal efficiency under the same operating condition. The enhanced performance with the new catalyst could be attributed to its significantly increased available surface active sites and improved mass transfer of reaction media, as a result of the special surface and structure properties of this new three-dimensional network-structured catalyst. Moreover, the new catalyst displays excellent stability and reusability for ibuprofen degradation over successive reaction cycles. The facile synthesis method and low-cost materials render the new catalyst high potential for industrial scaling up. With the combined advantages of high efficiency, high stability, and low cost, this study sheds new light for industrial applications of ozonation catalysts.

Electrospun-based TiO2 nanofibers for organic pollutant photodegradation: a comprehensive review

Titanium dioxide (TiO2) is commonly used as a photocatalyst in the removal of organic pollutants. However, weaknesses of TiO2 such as fast charge recombination and low visible light usage limit its industrial application. Furthermore, photocatalysts that are lost during the treatment of pollutants create the problem of secondary pollutants. Electrospun-based TiO2 fiber is a promising alternative to immobilize TiO2 and to improve its performance in photodegradation. Some strategies have been employed in fabricating the photocatalytic fibers by producing hollow fibers, porous fibers, composite TiO2 with magnetic materials, graphene oxide, as well as doping TiO2 with metal. The modification of TiO2 can improve the absorption of TiO2 to the visible light area, act as an electron acceptor, provide large surface area, and promote the phase transformation of TiO2. The improvement of TiO2 properties can enhance carrier transfer rate which reduces the recombination and promotes the generation of radicals that potentially degrade organic pollutants. The recyclability of fibers, calcination effect, photocatalytic reactors used, operation parameters involved in photodegradation as well as the commercialization potential of TiO2 fibers are also discussed in this review.

Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects

Produced water is the largest byproduct of oil and gas production. Due to the complexity of produced water, especially dissolved petroleum hydrocarbons and high salinity, efficient water treatment technologies are required prior to beneficial use of such waste streams. Photocatalysis has been demonstrated to be effective at degrading recalcitrant organic contaminants, however, there is limited understanding about its application to treating produced water that has a complex and highly variable water composition. Therefore, the determination of the appropriate photocatalysis technique and the operating parameters are critical to achieve the maximum removal of recalcitrant compounds at the lowest cost. The objective of this review is to examine the feasibility of photocatalysis-involved treatment for the removal of contaminants in produced water. Recent studies revealed that photocatalysis was effective at decomposing recalcitrant organic compounds but not for mineralization. The factors affecting decontamination and strategies to improve photocatalysis efficiency are discussed. Further, recent developments and future research prospects on photocatalysis-derived systems for produced water treatment are addressed. Photocatalysis is proposed to be combined with other treatment processes, such as biological treatments, to partially reduce total organic carbon, break down macromolecular organic compounds, increase biodegradability, and reduce the toxicity of produced water.

Complementary behavior of doping and loading in Ag/C-ZnTa2O6 for efficient visible-light photocatalytic redox towards broad wastewater remediation

This work reports on the simple fabrication of a silver loaded and carbon doped zinc tantalate (Ag/C-ZnTa₂O₆) photocatalyst with visible light photocatalytic activity toward broad wastewater remediation, including high photo-reduction of Cr(vi) (98.4% in 210 min), excellent photo-oxidation of tetracycline hydrochloride (94.7% in 210 min), and superior photo-degradation of multiple dyes (>99.0% within 210 min). The optimal photocatalytic performance of Ag/C-ZnTa₂O₆ is mainly due to the excellent visible light absorption capacity and superior electron-hole separation efficiency, which is ascribed to the complementary behavior between carbon doping and silver loading. Particularly, the generation of defects due to C-doping is greatly inhibited by Ag-loading, and the SPR effect of Ag nanoparticles is enhanced due to the obstruction of Ag⁺ by C doping.