Anthraquinones-based photocatalysis: A comprehensive review

In recent years, there has been significant interest in photocatalytic technologies utilizing semiconductors and photosensitizers responsive to solar light, owing to their potential for energy and environmental applications. Current efforts are focused on enhancing existing photocatalysts and developing new ones tailored for environmental uses. Anthraquinones (AQs) serve as redox-active electron transfer mediators and photochemically active organic photosensitizers, effectively addressing common issues such as low light utilization and carrier separation efficiency found in conventional semiconductors. AQs offer advantages such as abundant raw materials, controlled preparation, excellent electron transfer capabilities, and photosensitivity, with applications spanning the energy, medical, and environmental sectors. Despite their utility, comprehensive reviews on AQs-based photocatalytic systems in environmental contexts are lacking. In this review, we thoroughly describe the photochemical properties of AQs and their potential applications in photocatalysis, particularly in addressing key environmental challenges like clean energy production, antibacterial action, and pollutant degradation. However, AQs face limitations in practical photocatalytic applications due to their low electrical conductivity and solubility-related secondary contamination. To mitigate these issues, the design and synthesis of graphene-immobilized AQs are highlighted as a solution to enhance practical photocatalytic applications. Additionally, future research directions are proposed to deepen the understanding of AQs' theoretical mechanisms and to provide practical applications for wastewater treatment. This review aims to facilitate mechanistic studies and practical applications of AQs-based photocatalytic technologies and to improve understanding of these technologies.

Reusable Cu2-xS-modified masks with infrared lamp-driven antibacterial and antiviral activity for real-time personal protection

Disposable surgical masks are widely used by the general public since the onset of the coronavirus outbreak in 2019. However, current surgical masks cannot self-sterilize for reuse or recycling for other purposes, resulting in high economic and environmental costs. To solve these issue, herein we report a novel low-cost surgical mask decorated with copper sulfide (Cu2-xS) nanocrystals for photothermal sterilization in a short time (6 min). With the spun-bonded nonwoven fabrics (SNF) layer from surgical masks as the substrate, Cu2-xS nanocrystals are in-situ grown on their surface with the help of a commercial textile adhesion promoter. The SNF-Cu2-xS layer possesses good hydrophobicity and strong near infrared absorption. Under the irradiation with an infrared baking lamp (IR lamp, 50 mW cm-2), the surface temperature of SNF-Cu2-xS layer on masks can quickly increase to over 78 °C, resulting from the high photothermal effects of Cu2-xS nanocrystals. As a result, the polluted masks exhibit an outstanding antibacterial rate of 99.9999% and 85.4% for the Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus) as well as the inactivation of human coronavirus OC43 (3.18-log10 decay) and influenza A virus A/PR/8/34 (H1N1) (3.93-log10 decay) after 6 min irradiation, and achieve rapid sterilization for reuse and recycling. Therefore, such Cu2-xS-modified masks with IR lamp-driven antibacterial and antiviral activity have great potential for real-time personal protection.

Fabrication of Rechargeable Photoactive Silk Fibroin/Polyvinyl Alcohol Blend Nanofibrous Membranes for Killing Bacteria

Antibacterial materials that prevent bacterial infections and mitigate bacterial virulence have attracted great scientific interest. In recent decades, bactericidal polymers have been presented as promising candidates to combat bacterial pathogens. However, the preparation of such materials has proven to be extremely challenging. Herein, photoactive silk fibroin/polyvinyl alcohol blended nanofibrous membranes grafted with 3,3',4,4'-benzophenone tetracarboxylic dianhydride (G-SF/PVA BNM) were fabricated by an electrospinning technique. The premise of this work is that the G-SF/PVA BNM can store photoactive activity under light irradiation and release reactive oxygen species for killing bacteria under dark conditions. The results showed that the resultant G-SF/PVA BNM exhibited the integrated properties of an ultrathin fiber diameter (298 nm), good mechanical properties, robust photoactive activity and photo-store capacity, and great photoinduced antibacterial activity against E. coli and S. aureus (99.999% bacterial reduction with 120 min). The successful construction of blended nanofibrous membranes gives a new possibility to the design of highly efficient antibacterial materials for public health protection.

Surface-Immobilized Photoinitiators for Light Induced Polymerization and Coupling Reactions

Straightforward and versatile surface modification, functionalization and coating have become a significant topic in material sciences. While physical modification suffers from severe drawbacks, such as insufficient stability, chemical induced grafting processes efficiently modify organic and inorganic materials and surfaces due to covalent linkage. These processes include the "grafting from" method, where polymer chains are directly grown from the surface in terms of a surface-initiated polymerization and the "grafting to" method where a preformed (macro)-molecule is introduced to a preliminary treated surface via a coupling reaction. Both methods require an initiating species that is immobilized at the surface and can be triggered either by heat or light, whereas light induced processes have recently received increasing interest. Therefore, a major challenge is the ongoing search for suitable anchor moieties that provide covalent linkage to the surface and include initiators for surface-initiated polymerization and coupling reactions, respectively. This review containing 205 references provides an overview on photoinitiators which are covalently coupled to different surfaces, and are utilized for subsequent photopolymerizations and photocoupling reactions. An emphasis is placed on the coupling strategies for different surfaces, including oxides, metals, and cellulosic materials, with a focus on surface coupled free radical photoinitiators (type I and type II). Furthermore, the concept of surface initiation mediated by photoiniferters (PIMP) is reviewed. Regarding controlled radical polymerization from surfaces, a large section of the paper reviews surface-tethered co-initiators, ATRP initiators, and RAFT agents. In combination with photoinitiators or photoredox catalysts, these compounds are employed for surface initiated photopolymerizations. Moreover, examples for coupled photoacids and photoacid generators are presented. Another large section of the article reviews photocoupling and photoclick techniques. Here, the focus is set on light sensitive groups, such as organic azides, tetrazoles and diazirines, which have proven useful in biochemistry, composite technology and many other fields.

Daylight-Induced Antibacterial and Antiviral Nanofibrous Membranes Containing Vitamin K Derivatives for Personal Protective Equipment

During the development of antibacterial and antiviral materials for personal protective equipment (PPE), daylight active functional polymeric materials containing vitamin K compounds (VKs) and impacts of polymer structures to the functions were investigated. As examples, hydrophobic polyacrylonitrile (PAN) and hydrophilic poly(vinyl alcohol-co-ethylene) (PVA-co-PE) polymers were directly blended with three VK compounds and electrospun into VK-containing nanofibrous membranes (VNFMs). The prepared VNFMs exhibited robust photoactivity in generating reactive oxygen species (ROS) under both daylight (D65, 300-800 nm) and ultraviolet A (UVA, 365 nm) irradiation, resulting in high antimicrobial and antiviral efficiency (>99.9%) within a short exposure time (<90 min). Interestingly, the PVA-co-PE/VK₃ VNFM showed higher ROS production rates and better biocidal functions than those of the PAN/VK₃ VNFM under the same photoirradiation conditions, indicating that PVA-co-PE is a better matrix polymer material for these functions. Moreover, the prepared PVA-co-PE/VK₃ VNFM maintains its powerful microbicidal function even after five times of repeated exposures to bacteria and viruses, showing the stability and reusability of the antimicrobial materials. The fabrication of photoinduced antimicrobial VNFMs may provide new insights into the development of non-toxic and reusable photoinduced antimicrobial materials that could be applied in personal protective equipment with improved biological protections.

Daylight-Induced Antibacterial and Antiviral Cotton Cloth for Offensive Personal Protection

Cotton fabrics with durable and reusable daylight-induced antibacterial/antiviral functions were developed by using a novel fabrication process, which employs strong electrostatic interaction between cationic cotton fibers and anionic photosensitizers. The cationic cotton contains polycationic short chains produced by a self-propagation of 2-diehtylaminoehtyl chloride (DEAE-Cl) on the surface of cotton fibers. Then, the fabric (i.e., polyDEAE@cotton) can be readily functionalized with anionic photosensitizers like rose Bengal and sodium 2-anthraquinone sulfate to produce biocidal reactive oxygen species (ROS) under light exposure and consequently provide the photo-induced biocidal functions. The biocidal properties of the photo-induced fabrics (PIFs) were demonstrated by ROS production measurements, bactericidal performance against bacteria (e.g., E coli and L. innocua), and antiviral results against T7 bacteriophage. The PIFs achieved 99.9999% (6 log) reductions against bacteria and the bacteriophage within 60 min of daylight exposure. Moreover, the PIFs showcase excellent washability and photostability, making them ideal materials for reusable face masks and protective suits with improved biological protections compared with traditional PPE. This work demonstrated that the cationized cotton could serve as a platform for different functionalization applications, and the resulting fiber materials could inspire the development of reusable and sustainable PPE with significant bioprotective properties to fight the COVID-19 pandemic as well as the spread of other contagious diseases.

Daylight-Active Cellulose Nanocrystals Containing Anthraquinone Structures

Antimicrobial and antiviral materials have attracted significant interest in recent years due to increasing occurrences of nosocomial infections and pathogenic microbial contamination. One method to address this is the combination of photoactive compounds that can produce reactive oxygen species (ROS), such as hydrogen peroxide and hydroxyl radicals to disinfect microbes, with carrier materials that meet the application requirements. Using anthraquinone (AQ) and cellulose nanocrystals (CNCs) as the photoactive and carrier components, respectively, this work demonstrated the first covalent incorporation of AQ onto CNCs. The morphology and the photoactive properties were investigated, revealing the structural integrity of the CNCs and the high degree of photoactivity of the AQ-CNC materials upon UVA exposure. The AQ-CNCs also exhibited an unexpected persistent generation of ROS under darkness, which adds advantages for antimicrobial applications.

Photopatternable and photoactive hydrogel for on-demand generation of hydrogen peroxide in cell culture

Oxidative stress, largely mediated by reactive oxygen species (ROS), is a nearly ubiquitous component in complex biological processes such as aging and disease. Optimal in vitro methods used in elucidating disease mechanisms would deliver of low levels of hydrogen peroxide, emulating the in vivo pathological state, but current methods are limited by kinetic stability or accurate measurement of the dose administered. Here we present an in vitro platform that exploits anthraquinone catalysts for the photocatalytic production of hydrogen peroxide. This system can be dynamically tuned to provide constant generation of hydrogen peroxide at a desired physiologic rate over at least 14 days and is described using a kinetic model. Material characterization and stability is discussed along with a proof-of-concept in vitro study that assessed the viability of cells as they were oxidatively challenged over 24 h at different ROS generation rates.

Fabrication and evaluation of nanofibrous membranes with photo-induced chemical and biological decontamination functions

Hydrophilic nanofibrous membranes with photo-induced self-cleaning functionality were successfully prepared. Under UVA irradiation, these membranes are able to generate reactive oxygen species, attributing to the observed photo-induced chemical and biological decontamination functions.

Antimicrobial functions on cellulose materials introduced by anthraquinone vat dyes

Many anthraquinone compounds have exhibited light-active properties in solutions and on materials under UVA or fluorescent light exposure. Two anthraquinone derivatives were incorporated onto cotton fabrics by a vat dyeing process. The dyed fabrics demonstrated light-induced biocidal functions, and the functions were durable against laundering and long-term light exposure. The structures and surface morphologies of the dyed fabrics were examined by using fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). Mechanical properties of the fabrics were measured by using a tensile tester. The results revealed that the anthraquinone compounds have different light-activities, resulting in different surface and mechanical impacts on the cotton cellulose.