UV-B Region Research Articles

In situ tailoring of Ag-doped-TiO2/TPMP/cotton nanocomposite with UV-protective, self-sterilizing and flame-retardant performance for advanced technical textiles

Herein, we present a novel approach to the development of a multifunctional, UV-protective, photocatalytic, antimicrobial and flame-retardant nanocomposite fabric surface. Using a sol–gel/hydrothermal approach, a phosphorus-based flame-retardant 3-(trihydroxysilyl)propyl methylphosphonate (TPMP) in combination with Ag-doped TiO2 was applied to the surface of cotton fibers for the first time, using an aqueous AgNO3 solution as the dopant. The modified cotton fabrics were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS) and X-ray diffraction spectroscopy (XRD) to confirm the successful application of Ag-TiO2 and TPMP on the cotton fabric by analyzing the surface morphology, chemical composition, chemical bonding and crystal structure. The functional properties of the modified cotton fabric were determined by measuring the UV protection factor (UPF), burning behavior and thermo-oxidative stability, as well as antibacterial activity against Escherichia coli and Staphylococcus aureus. The results show the formation of a unique nanocomposite matrix of TPMP–polysiloxane on the surface of cotton fibers with well-distributed Ag-TiO2. The formation of TiO2/Ag2O particles on the surface of cellulose fibers was also confirmed. The synergism between all components of the nanocomposite resulted in excellent UV protection in the UVA and UVB region, with a UPF of 50+, self-sterilizing activity against both tested bacteria and enhanced thermo-oxidative stability. Therefore, the novel approach proposed herein is promising for the development of multifunctional, protective surfaces for advanced technical textiles.

ZnO quantum dots-diacetylenes-zinc(II) nanocomposites for colorimetric detection of ultraviolet-B light: the size effects

Polydiacetylenes (PDAs) are color-responsive materials that have shown potential as colorimetric sensors for detecting various classes of analytes. However, the utilization of PDAs for sensing ultraviolet-B light (UVB) is rare. This contribution introduces a facile method for enhancing the UVB-responsive property of PDAs by incorporating zinc oxide (ZnO) quantum dots (QDs). We explore the size effects of ZnO QDs/nanoparticles and diacetylene (DA) monomers on the sensitivity of the resultant nanocomposites to UVB light. Interestingly, the sensitivity of nanocomposites to UV light with different wavelengths can be controlled by adjusting the size of ZnO nanoparticles. We have found that the incorporation of ZnO QDs with diameters ranging from 2.2 to 3.8 nm drastically increases the sensitivity to UVB light. In addition, fine-tuning of the UVB sensitivity can be achieved by varying alkyl chain lengths of the DA monomers. The colorimetric response of nanocomposites to specific UVB regions can be obtained by adjusting the band gap of ZnO QDs. This property allows their utilization as colorimetric sensors for detecting UVB doses in sunlight and other sources. Colorimetric UVB sensors can be fabricated in different forms including smart ink sensors, free-standing flexible sensors, paper-based sensors, and hydrogel-based sensors.

Developing Thermally Stable Defect-Assisted Phosphors of BaSc2Ge3O10:Bi3+ for Pc-UV-LEDs Applications.

Current ultraviolet (UV) light sources are dominated by blacklights that contain mercury vapor. Improper disposal or accidental breakage of these lamps can lead to serious pollution. Phosphor-converted light-emitting diodes (pc-UV-LEDs) have the potential to replace these mercury-containing lamps, making them more environmentally friendly. To improve the adjustability of the UV emission and reduce production cost, a series of UV-emitting phosphors were developed by introducing Bi3+ in BaSc2Ge3O10 (BSGO) which has a broad bandgap of 5.88 eV. The phosphor exhibits a negative thermal quenching effect that results from thermally activated defects. Despite this, the emission intensity of the phosphor sustains up to 107% at 353 K and 93% at 473 K compared to the intensity at 298 K. The internal quantum efficiency and the external quantum efficiency reach 81.0 and 49.32%, respectively, under 305 nm excitation. A pc-UV-LEDs were fabricated by combining the phosphor with a chip. The resulting device emits a broad band ranging from 295 nm to 450 nm, covering part of the UVB (280 nm ∼ 315 nm) and UVA (315-400 nm) regions. Our work has the potential to promote the replacement of current blacklights, including high-pressure mercury lamps and fluorescent low-pressure mercury lamps, by pc-UV-LEDs in applications such as bug zappers and tanning beds. Moreover, the phosphor exhibits desirable long persistent luminescence, which extends its prospect of applications.

Synthesis, structural, photoluminescence, ultraviolet blocking and antibacterial performances of Ba-doped ZnO nanostructures

In the current experimental work, pure ZnO and Ba-doped ZnO nanorods have been prepared by implementing a facile wet chemical technique. XRD study reveals the formation of the hexagonal wurtzite phase of pure ZnO and Ba-doped ZnO nanorods. Interestingly, Ba-doped ZnO nanorods show very good absorption in the UVA (93% at 351 nm), UVB (90% at 300 nm) and UVC (61% at 220 nm) regions. The obtained results of the UV–visible absorbance study validate in such a way that the Ba-doped ZnO nanorods could be a better bet to be utilized as a UV blocker for the next generation of UV shielding materials. The Photoluminescence spectrum of Ba-doped ZnO nanoparticles reveals widespread UV–Visible bands between 350 and 600 nm. Also, the zone of inhibition is found to be 15 nm for both bacterial strains S.aures and E.coli and implies excellent antibacterial activity. Interestingly, the outcome as observed in the zone of inhibition towards S. aureus and E. coli in the present study is found to be higher than many doped ZnO and Ba-doped metal oxide nanostructures. The observed experimental results via the aforementioned characterizations imply that the synthesized samples possess the potential ingredients required for the applications related to the field of health care.

Bioactive film based on chitosan incorporated with cellulose and aluminum chloride for food packaging application: Fabrication and characterization

Bioactive packaging materials are developed responding to the considerable environmental and human health risks caused by plastic packaging. In this study, a new generation of ternary composite films based on aluminum chloride (AlCl3)/chitosan (CS)/cellulose (Cel) was fabricated for use as bioactive packaging. FTIR, XRD, SEM and TGA results confirmed AlCl3/CS incorporation with Cel and homogeneous distribution in the composites. UV–Vis spectrometry of the ternary composite films showed a lack of light transmission in the UVA and UVB regions, indicating the highest protective efficiency of the composite film. The AlCl3/CS/Cel composite films manifested higher water uptake in comparison with CS/Cel film, thus AlCl3 improved the hydrophilicity and mechanical properties of AlCl3/CS/Cel composite films. Moreover, the AlCl3/CS/Cel composite exhibited better antimicrobial activity against Gram-positive and Gram-negative bacteria than the pristine film. These results suggested that the bioactive AlCl3/CS/Cel film utilized in this study might be a promising material in food packaging to prolong the shelf life and improve food safety.

Sustainable acid hydrotropic fractionation for bamboo-based nanofilms with unparalleled hydrophobicity and UV resistance

Bamboo, as an important biomass raw material, has a very favorable prospect for Nature-based Solution. Here we provide a method to prepare bamboo-based lignocellulosic nanofibrils (LCNFs) and films with excellent impedance performances by p-toluenesulfonic acid (p-TsOH) under mild condition. The combined delignification factor (CDF) and combined hydrolysis factor (CHF) were introduced to regulate the hydrolysis severity. The resultant LCNFs with uniform diameter retained a plentiful reactivity without surface functional group changing. The ascendant thermal stability (Tmax > 360 °C) of the LCNFs were also obtained. The films made by the LCNFs can block about 99 % UV light with transparency greater than 50 % which exhibited remarkable UV resistance in both UVA and UVB regions. Furthermore, the films presented excellent hydrophobic stability which showed large contact angles (water, 89–99°) and maintained at 64° after 300 s. These properties make bamboo-based materials substitute bamboo for plastics and can be used in aviation, construction, automotive industry, packaging and many other fields, conforming to international initiatives.

(MgO)60: A magic cluster active in UV range under DFT study

Density functional theory (DFT) is used to investigate the minimum energy geometries for (MgO)6n (n = 8 to 11) nanoclusters series. Moreover, a new ultraviolet active magic cluster, viz. (MgO)60 in addition to our reported magic cluster (MgO)42 elsewhere. Upon investigation on the considered series on their electronic properties like HOMO-LUMO gap (HLG), electron affinity (EA), ionization potential (IP), electrophilicity index (ω), chemical hardness (η), and energy gain of formation (ΔE), (MgO)60 is identified as a ‘magic’ nanocluster. Interestingly, as the stoichiometry of (MgO) in (MgO)6n series increases with n, the gain in energy (ΔE) of MgO clusters demonstrates an increasing pattern, identifying (MgO)60 as a ‘magic’ nanocluster. Further, optical absorption spectra show that (MgO)60 cluster is active in the UV-B region. The identified UV active (MgO)60 nanocluster may find useful applications in the field of sensors, energy storage, and catalysis.

Investigation of UV emission and energy transfer process in Ce3+, Gd3+, Pr3+ and their combination doped nano crystallite La2O3 phosphors

Despite being a harmful radiation, there are many useful applications of UV radiation. This includes its use in the biomedical field. Hence, it is required to generate the UV radiation with desired characteristics. In this work, seven rare earth based compounds i. e. 1 % Ce3+: La2O3, 1 % Gd3+: La2O3, 1 % Ce3+ – 1 % Gd3+: La2O3, 2 % Ce3+ – 1 % Gd3+: La2O3, 1 % Pr3+: La2O3, 1 % Pr3+ – 1 % Gd3+: La2O3, and 2 % Pr3+ – 1 % Gd3+: La2O3 have been synthesized to study their UV emission properties and related energy transfer process. The synthesis process is also relatively simple and eco-friendly, with fewer elements used and giving a higher yield of products. The XRD & EDAX analysis reveals that the obtained compounds possess high purity and are in hexagonal phase state with crystallite size in the nanometer range. The bandgap and refractive index were calculated from absorption spectra obtained by UV – Visible spectrometry. From the PL Spectroscopy, the emission of 1 % Gd3+: La2O3 falls in UVB region, while that of 1 % Ce3+: La2O3 & 1 % Pr3+: La2O3 – in UVA region. Both, UVA and UVB emission were recorded in 1 % Ce3+ – 1 % Gd3+: La2O3, 2 % Ce3+ – 1 % Gd3+: La2O3 due to the resonance transfer and radiative transfer of energy from Ce3+ ion to Gd3+ ion. In 1 % Pr3+ – 1 % Gd3+: La2O3 and 2 % Pr3+ – 1 % Gd3+: La2O3, the emission was obtained in UVA with very low intensity and another intense peak was observed in the visible region due to the energy transfer from Gd3+ ion to Pr3+ ion. The parameters like redshift D, centroid shift Ɛc and crystal field splitting Ɛcfs were calculated for Ce & Ce – Gd based La2O3 compounds. Based on these calculations, the model for energy levels of Ce3+ in La2O3 is proposed.

Reinforcement of V2O5 nanoparticle in polyaniline to improve the optical and UV- shielding properties

The aim of the study is to fulfil the prerequisite of the scientific community for the development of UV protective materials, especially UV shielding coatings with visible transparency but block plentiful UV light. The present study contributed to the same approach by preparing conducting polymer nanocomposites of V2O5: PANI by polymerization of V2O5 with PANI using ammonium persulphate as an oxidant. Here, we report the UV-shielding efficiency and visible light transmittance of V2O5: PANI nanocomposites where V2O5 acts as a UV absorber. UV–visible study shows that different optical parameters changed considerably after doping and facilitate UV shielding efficiency of the prepared nanocomposites in the area of interest. The weight concentration of 30% V2O5 in the PANI matrix showed a 93% increase in UV shielding efficiency with respect to PANI in the UVB region. Distinct changes including red shift, narrowing of the band gap, better polarizability, tuned refractive index as well as dissipation factor could provide valuable insight into the design and development of new and superior UV shielding materials.

Synthesis of Planar-Type ZnO Powder in Non-Nano Scale Dimension and Its Application in Ultraviolet Protection Cosmetics

ZnO is one of the most widely used inorganic sunscreens, owing to its fine particle size and UV light shielding capability. However, powders at nanosizes can be toxic and cause adverse effects. The development of non-nanosized particles has been slow. The present work investigated synthesis methods of non-nanosized ZnO particles for ultraviolet protection application. By altering the starting material, KOH concentration, and input speed, the ZnO particles can be obtained in different forms, including needle type, planar type, and vertical wall type. Cosmetic samples were made by mixing different ratios of synthesized powders. The physical properties and the UV blockage efficacy of different samples were evaluated using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer (PSA), and ultraviolet/visible (UV/Vis) spectrometer. The samples with 1:1 ratio of needle-type ZnO and vertical wall-type ZnO exhibited superior light blocking effect owing to improved dispersibility and prevention of particle agglomeration. The 1:1 mixed sample also complied with the European nanomaterials regulation due to the absence of nanosized particles. With superior UV protection in the UVA and UVB regions, the 1:1 mixed powder showed potential to be used as a main ingredient in UV protection cosmetics.

Aluminum Quantum Dots with Surface Controlled Blue-UV Photoluminescence

Aluminum quantum dots (AlQDs) are an emerging class of optical material due to their unique photoluminescence in the ultraviolet waveband. Herein, a strategy is presented to control their photoluminescence emission. The synthesized AlQDs displayed photoluminescence from the UV-B region (<320 nm) to the near-ultraviolet region (∼425 nm) and high quantum yields. Our investigation revealed that surfactants and phosphonic acids (PAs) were competitively bound to the surface of AlQDs, and this was affected by the space volume of surfactants and charge of head groups. The steady-state and time-resolved spectroscopic data suggested the emission properties of AlQDs mainly originated from the surface-mediated states. The red-shifting of emission peak was a result of increased amount of PAs on the surface of AlQDs, which could be related to the surface oxygen presented in both ligands and surfactants. Overall, this study indicates a method to control the photoluminescence of AlQDs by changing the surfactants and surface ligands, which is fundamental to their applications in photonics and applications to energy and environment, in addition to biomedicine.

A self-powered and broadband UV PIN photodiode employing a NiOx layer and a β-Ga2O3 heterojunction

Crucial commercial and space applications require the detection of broadband ultraviolet (UV) rays spanning from UV-A to UV-C. In this study, the authors demonstrate a broadband UV photodetector employing a p-type NiOx layer and an n-type β-Ga2O3 heterostructure in PIN configuration for the first time. Simulations are conducted to optimize the doping concentration and thickness of the NiOx layer, ensuring that (a) a reasonable depletion width is maintained within the NiOx layer for UV-A and UV-B light absorption; (b) anode ohmic contacts are formed on the nondepleted NiOx film, and (c) >70% of the UV-C light is absorbed by β-Ga2O3. The optimized NiOx/β-Ga2O3 PIN photodiode exhibits good responsivity to incident light wavelengths in the UV-A, UV-B, and UV-C regions. While the NiOx layer is considered to be responsible for providing good photoresponsivity in the UV-A and UV-B regions, a highly resistive (near-intrinsic) β-Ga2O3 layer is required for the absorption of incident UV-C light. A record detectivity of >1011 cm Hz0.5 W−1 for the UV-B and UV-C regions and >1010 cm Hz0.5 W−1 for the UV-A region is observed in the NiOx/β-Ga2O3 heterostructure PIN photodiode during the self-powered operation. The results presented in this study are promising and instigate device design strategies for (ultra)wide bandgap semiconductor-based broadband UV PIN photodetectors.

Blue-to-UVB Upconversion, Solvent Sensitization and Challenging Bond Activation Enabled by a Benzene-Based Annihilator.

Several energy-demanding photoreactions require harsh UV light from inefficient light sources. The conversion of low-energy visible light to high-energy singlet states via triplet-triplet annihilation upconversion (TTA-UC) could offer a solution for driving such reactions under mild conditions. We present the first annihilator with an emission maximum in the UVB region that, combined with an organic sensitizer, is suitable for blue-to-UVB upconversion. The annihilator singlet was successfully employed as an energy donor in subsequent FRET activations of aliphatic carbonyls. This hitherto unreported UC-FRET reaction sequence was directly monitored using laser spectroscopy and applied to mechanistic irradiation experiments demonstrating the feasibility of Norrish chemistry. Our results provide clear evidence for a novel blue light-driven substrate or solvent activation strategy, which is important in the context of developing more sustainable light-to-chemical energy conversion systems.

Withania somnifera-derived carbon dots protect human epidermal cells against UVB-induced cell death and support growth factor-mediated wound healing.

Solar radiation comprising UVA and UVB regions is considered a skin-damaging factor inducing inflammation, oxidative stress, hyperpigmentation, and photo-aging. Photoluminescent carbon dots (CDs) were synthesized from the root extract of a Withania somnifera (L.) Dunal plant and urea, using a one-step microwave method. These Withania somnifera CDs (wsCDs) were 14.4 ± 0.18 d nm in diameter and presented photoluminescence. UV absorbance showed the presence of π-π* (C[double bond, length as m-dash]C) and n-π* (C[double bond, length as m-dash]O) transition regions in wsCDs. FTIR analysis indicated the presence of nitrogen and carboxylic functional groups on the surface of wsCDs. HPLC analysis of wsCDs showed the presence of withanoside IV, withanoside V, and withanolide A. The wsCDs were found to be biocompatible in human skin epidermal (A431) cells and hindered UVB irradiation-induced loss of metabolic activity and oxidative stress. The wsCDs supported rapid dermal wound healing through augmented TGF-β1 and EGF gene expression levels in A431 cells. Finally, wsCDs were found to be biodegradable through a myeloperoxidase-catalyzed peroxidation reaction. The study concluded that under in vitro conditions, Withania somnifera root extract-derived biocompatible carbon dots provided photo-protection against UVB-stimulated epidermal cell damage and supported rapid wound healing.

Factors to control the alignment of surface-treated titanium dioxide powders to maximize performance of sunscreens.

Titanium dioxide powders are contained in a large class of colour cosmetics and sunscreen formulas. When they are used, the formation of a uniform functional powder layer on the skin is an important factor to show their functionality, such as aesthetic and UV protection. Attempts were made to extract the factors that affect the UV shielding ability of the deposited powder layer. Seven kinds of surface treatments were conducted on nano-sized titanium dioxide powder to modify the surface characteristics. Dispersion samples were prepared by mixing these powders with liquids, such as mixed solutions of cyclopentasiloxane, isododecane, coconuts alkane and dimethicone using a disperser and a bead mill. The dispersions were applied using an applicator on cellulose triacetate film, polycarbonate film and polymethyl pentene film. Laser microscope observation and micro-gloss glossmeter analysis were carried out to assess the flatness of the deposited powder layers, and the UV shielding ability was evaluated using SPF analyser. Factors whose influences on the structure and UV shielding ability of the deposited powder layer being analysed were pseudo-HLB of the powders, liquids for preparing the dispersions and material of the substrates. Higher UV shielding ability was attained when powders having pseudo-HLB at around 6 were employed independent from the kinds of liquids and substrates. Flatness of the deposited layer was found to enhance the UV shielding ability of the UV-B region, while that of the UV-A region was scarcely influenced by the flatness. Employing lower surface tension liquids for preparing the dispersions and materials exhibiting lower polar components of surface free energy as substrates tended to enhance the UV shielding ability. Surface treatments conducted on the powders in this study were found to change UV shielding ability, especially UV-B shielding ability, and the relation between pseudo-HLB and UV shielding ability was scarcely influenced by the kinds of liquids. Both surface tension of liquids and the polar component of surface free energy of substrates affected the UV shielding ability. It was suggested that pseudo-HLB calculated based on chemical structure becomes useful information to choose optimum surface treatment to make uniform powder alignment independent from the surrounding environment.

Toward the Scalable Fabrication of Fully Bio-Based Antimicrobial and UVB-Blocking Transparent Polylactic Acid Films That Incorporate Natural Coatings and Nanopatterns.

Microbial transmissions via membrane surface and single-use plastic-induced pollution are two urgent societal problems. This research introduces a scalable fabrication strategy for fully biobased antibacterial and ultraviolet-B block polylactic acid (PLA) films integrating natural coatings and nanopatterns via ultrasonic atomization spray coating and thermal nanoimprinting lithography (TNIL) techniques, respectively. Tannic acid (TA) and gallic acid (GA) were formulated prior to TNIL using anode aluminum oxide template. Results reveal that TA and GA inks display intense adsorption in the UVB region. Plasma increases the hydrophilicity of PLA films for fast spreading of ink droplets. Micron-sized pillars observed on film confirm the successful structural replication. TA-coated PLA films display higher transparency than GA-coated ones. Nanopatterned PLA films have a modest antibacterial resistance of c. 45% against Escherichia coli. TA/GA coatings, however, impart PLA films with a bacterial reduction rate of over 80%. The integration of a TA or GA coating with nanopatterns further promotes the antibacterial rate up to 98%. The cytocompatibility of TA and GA demonstrates that the engineered film can potentially be applied as food packaging. Finally, a continuous mass production strategy is proposed along with an outline of the associated challenges and costs. This study provides a scalable strategy to the sustainable development of eco-benign and functional films.

Influence of natural exposure on castor oil based polyurethane reinforced with waste tire rubber

Waste tire rubber (WTR) has been extensively generated worldwide due to mobility needs growth. About 1.5 billion units are generated annually, constantly discharged in the environment with a few reusability alternatives. Therefore, rubber recovery methods and these residues’ transformation into a cost-effective product have gained attention. Aiming to minimize the usage of fossil resources and contributes to a circular economy, it was analyzed the usage of WTR particles (5–20% by weight) in castor oil-based polyurethane foams under natural aging to promote a holistic view of all factors involved in the performance of the foams. Morphological, thermal, chemical, and mechanical properties were determined before and after exposure to open air to observe the impact of photo-oxidation and hydrolysis. The increase in viscosity of pre-polymer during the rubber loading produced greater density foams with smaller cell sizes than neat PU, in which the average cell size increased after the weathering. The rubber contributes to enhancing the compressive behavior in the non-exposed samples. After exposure, the results suggest that degradation may act to increase the crosslinking density even with the presented structural changes such as yellowing and voids. Regarding thermal stability, the rubber promotes a slight decay in the ability to resist a heat flow before and after weathering. Still, the char yield increased, showing a possibility of better fire retardancy for composites. FTIR and UV–vis showed chemical structure changes as Photo-Fries network rearrangement, Norrish I random chain scission, and Norrish II β-scission. Besides, UV–vis revealed the maximum absorbance in the UVB region, showing that the PU reinforced by WTR can be a promising material for civil coatings.

Multicolor Emitting Carbon Dot-Reinforced PVA Composites as Edible Food Packaging Films and Coatings with Antimicrobial and UV-Blocking Properties.

Active food packaging has become attractive because of the possibility to provide a longer shelf-life by loading functional agents into the packages to maintain the quality of food products. Herein, photoluminescent and transparent polyvinyl alcohol (PVA)-based composites embedding multicolor fluorescent carbon dots (CD/PVA) were prepared by the solvent casting method. The prepared CDs emit a strong and stable fluorescence in solution while the CD/PVA composite films were transparent, flexible, and showed UV-blocking activity with a strong fluorescence emission. Blue color-emitting CDs showed the highest UV blockage at UVA (87.04%), UVB (87.04%), and UVC (92.22%) regions while PVA alone absorbed only less than 25% of the light in all UV regions. UV blockage capacity was shown to be decreased by half, in line with the emission color shift from blue to red. Thermal properties of the PVA film were improved by the addition of CDs to the polymer, and in vitro cell viability tests showed that none of the CDs were cytotoxic against the human lung fibroblast healthy cell line (MRC-F cells) when integrated into the PVA. The antimicrobial activity of CD/PVA nanofilms was qualitatively determined. The prepared films exhibited good antimicrobial activity against both Gram-positive and Gram-negative bacteria with mild antioxidant and metal chelating activity, and significant inhibition of biofilm formation with a strong link with emitted color and the concentration of the composites. Green- and red-emitting CD/PVA with the highest antimicrobial activity were then analyzed and compared with the plane PVA employing their effect on the shelf-life of strawberries as a model for perishable foods. Fresh strawberries dip coated with CD/PVA and PVA were monitored over time, and virtual evaluations showed that CDs/PVA film coating resulted in reduced weight and moisture loss and significantly inhibited the fungal growth and spoiling for over 6 days at RT and 12 days at fridge conditions maintaining the visual appearance and natural color of the fruit. The findings in this work indicated the potential of reported CD as non-cytotoxic, UV-blocking antimicrobial additives for the development of edible coatings and packages for their use in the food industry, as well as pharmaceutical and healthcare applications.

Revisiting the mechanisms of nitrite ions and ammonia removal from aqueous solutions: photolysis versus photocatalysis.

Nitrite ions and ammonia are widespread forms of inorganic water pollutants. Nevertheless, the mechanisms of their photolytic and photocatalytic reactions under UV-A irradiation are still fully undisclosed, particularly, at different pH values under aerobic and inert atmospheres. Herein, we have studied the photolytic decomposition of nitrite ions under different conditions using 365nm UV-A LED as a light source instead of mercury lamps that emit photons in the UV-B region and generate a lot of heat. The results indicated that the rate of nitrite disproportionation in the dark at pH ≤ 3.0 is remarkably high relative to the rate of the photolytic decomposition. At pH ˃ 3, the photolytic reaction is negligible and nitrite ions showed considerable stability. In contrast, the photocatalytic oxidation of nitrite ions over TiO2 photocatalysts, namely, TiO2P25, TiO2UV100, and TiO2 anatase/brookite mixture proceeds at pH ˃ 3.0. TiO2 P25 exhibited the highest photocatalytic activity at pH 5. Interestingly, the photolytic simultaneous removal of nitrite ions and ammonia was possible at pH 9.0 in the absence of oxygen (Ar atmosphere). A 42.69 ± 0.66%, 27.75 ± 1.7%, and 32.74 ± 0.59% of nitrogen calculated based on nitrite, ammonia, and both of them, respectively, can be removed after 6h of UV-A irradiation. The selectivity of N2 evolution was 77.6%. The nitrogen removal rate was significantly reduced in the presence of TiO2 photocatalyst evincing that TiO2 photocatalysis is applicable for nitrite ions oxidation, whereas the photolytic process is better suited for the simultaneous removal of nitrite ions and ammonia.

Nature-inspired construction of iridescent CNC/Nano-lignin films for UV resistance and ultra-fast humidity response

Exploration of functional materials based on sustainable and renewable biomolecules has been of much interest. Herein, nature-inspired photonic films were proposed by incorporation of bio-based lignin nanoparticles (LNPs) into chiral nematic cellulose crystals (CNCs). Evaporation induced self-assembly (EISA) formed oriented and layered structure of the nanocomposites iridescent films with enlarged helix pitches by intercalation of higher amounts of LNPs. Decreased crystallite sizes and expanding layer gaps indicated the homogeneous distribution and hydrophobic interactions between CNCs and LNPs. Distinguished UV absorption capabilities with over 90 % shielding capabilities in UVB region and increased hydrophobicity with the contact angle of 75° were achieved for the composite films due to the presence of hydrophobic lignin. The proposed optical films also showed outstanding cytocompatibility owing to all-natural components introduced into the materials, which may display great potentials in many fields such as stimuli sensing, anti-counterfeiting and wearable devices.