The radical impact of oxygen on prokaryotic evolution-enzyme inhibition first, uninhibited essential biosyntheses second, aerobic respiration third.

Molecular oxygen is a stable diradical. All O2-dependent enzymes employ a radical mechanism. Generated by cyanobacteria, O2 started accumulating on Earth 2.4 billion years ago. Its evolutionary impact is traditionally sought in respiration and energy yield. We mapped 365 O2-dependent enzymatic reactions of prokaryotes to phylogenies for the corresponding 792 protein families. The main physiological adaptations imparted by O2-dependent enzymes were not energy conservation, but novel organic substrate oxidations and O2-dependent, hence O2-tolerant, alternative pathways for O2-inhibited reactions. Oxygen-dependent enzymes evolved in ancestrally anaerobic pathways for essential cofactor biosynthesis including NAD+, pyridoxal, thiamine, ubiquinone, cobalamin, heme, and chlorophyll. These innovations allowed prokaryotes to synthesize essential cofactors in O2-containing environments, a prerequisite for the later emergence of aerobic respiratory chains.

Polymer Network Film with Double Reflection Bands Prepared Using a Thermochromic Cholesteric Liquid Crystal Mixture.

Cholesteric liquid crystal polymer network (CLCN) films with a single reflection band have found applications for decoration and anticounterfeiting. The CLCN films with double reflection bands were more suitable for these applications. Herein, they were prepared by using thermochromic cholesteric liquid crystals (CLCs) through a two-step photopolymerization approach. At the first step, due to oxygen inhibition, the CLC monomers near the substrate surface were polymerized at a certain temperature. At the second step, those near the air were polymerized at another temperature. The wavelengths of these two reflection bands of the CLCN film were dominated by the two polymerization temperatures. Based on this approach, patterns with composite colors were prepared, which were suitably applied for decoration. Moreover, a double-layered CLCN film with a broad reflection band was prepared that could potentially be applied for displays.

Polymer-Stabilized Cholesteric Liquid Crystal Films with Double Reflection Bands Prepared Based on the Competition between Photopolymerization and Photoisomerization.

Composite colors have been widely found in nature. Herein, polymer-stabilized cholesteric liquid crystal (PSCLC) films with composite structural colors were prepared through a one-step photopolymerization approach. The CLC mixtures were prepared using a mixture of acrylates and a mixture of two chiral dopants. One of the chiral dopants is polymerizable, and the other one is photoisomerizable. After photopolymerization, the PSCLC films with double Bragg reflection bands were obtained on the surface of a substrate. The competition between the photopolymerization of the acrylates and the photoisomerization of the chiral dopant was proposed to drive the formation of the double reflection bands. Without oxygen inhibition, the polymerization of the acrylates near the substrate surface was carried out. However, due to oxygen inhibition, the polymerization of the acrylates near the air was retarded. Then, the photoisomerization of the chiral dopant was carried out prior to the polymerization of the acrylates. The wavelengths of the double reflection bands were tunable by changing the concentrations of the acrylates and chiral dopants and the polymerization temperature. Colorful patterns with composite structural colors were prepared, which were suitable for decoration and anti-counterfeiting.

Designing Superlubricious Hydrogels from Spontaneous Peroxidation Gradients.

Hydrogels are hydrated three-dimensional networks of hydrophilic polymers that are commonly used in the biomedical industry due to their mechanical and structural tunability, biocompatibility, and similar water content to biological tissues. The surface structure of hydrogels polymerized through free-radical polymerization can be modified by controlling environmental oxygen concentrations, leading to the formation of a polymer concentration gradient. In this work, 17.5 wt % polyacrylamide hydrogels are polymerized in low (0.01 mol % O2) and high (20 mol % O2) oxygen environments, and their mechanical and tribological properties are characterized through microindentation, nanoindentation, and tribological sliding experiments. Without significantly reducing the elastic modulus of the hydrogel (E* ≈ 200 kPa), we demonstrate an order of magnitude reduction in friction coefficient (from µ = 0.021 ± 0.006 to µ = 0.002 ± 0.001) by adjusting polymerization conditions (e.g., oxygen concentration). A quantitative analytical model based on polyacrylamide chemistry and kinetics was developed to estimate the thickness and structure of the monomer conversion gradient, termed the "surface gel layer". We find that polymerizing hydrogels at high oxygen concentrations leads to the formation of a preswollen surface gel layer that is approximately five times thicker (t ≈ 50 µm) and four times less concentrated (≈ 6% monomer conversion) at the surface prior to swelling compared to low oxygen environments (t ≈ 10 µm, ≈ 20% monomer conversion). Our model could be readily modified to predict the preswollen concentration profile of the polyacrylamide gel surface layer for any reaction conditions─monomer and initiator concentration, oxygen concentration, reaction time, and reaction media depth─or used to select conditions that correspond to a certain desired surface gel layer profile.

Light Intensity-Selective Photopolymerization and Photoisomerization for Creating Colorful Polymer-Stabilized Cholesteric Liquid Crystal Patterns.

Polymer-stabilized cholesteric liquid crystal (PSCLC) films have been widely studied for their application as sensors, polarizers, and reflective windows. However, the preparation of programmable and colorful patterns based on the structural color is still challenging. Herein, the photochromic CLC mixtures were prepared by adding a photoisomerizable chiral additive (CA) and a photoinitiator in the nematic liquid crystal LC242. Under UV irradiation with weak intensity, photoisomerization of the CA was carried out and photopolymerization was suppressed by oxygen inhibition. With extending the irradiation time, the helical pitch of the CLC film increased and the selective Bragg reflection band tended to redshift. Under strong UV irradiation, oxygen inhibition was overcome and photopolymerization dominates the reaction. Therefore, the colorful-patterned PSCLC films were able to be prepared using masks. The results shown here not only give us a better understanding of the effect of oxygen inhibition but also lay the foundations for practical applications such as decoration and optical devices.

Evaluating oxygen shielding effect using glycerin or vacuum with varying temperature on 3D printed photopolymer in post-polymerization.

The photosensitive resin used in additive manufacturing is cured by free radical polymerization by UV irradiation. However, undesired reaction with oxygen during polymerization inhibits polymerization and results in an under-cured polymer. Therefore, in this study, the hypothesis that successful oxygen shielding in the post-polymerization step could affect the properties of the final polymer was tested. 3D printed specimens using denture base resin were post polymerized either by immersion in glycerin for oxygen shielding (GL group) or placed in a medium-low vacuum chamber at 5 × 10-2 Torr (VA group). Specimens cured with no additional conditioning served as the control (CON group). To consider the effect of temperature, all groups were additionally compared with 80 °C and without an increase in temperature (room temperature) during post-polymerization. Fourier transform infrared spectroscopy was used to measure the monomer conversion ratios between different groups. In addition, the mechanical properties were quantified by the micro-hardness, flexural strength, and elasticity of the surface, and the water sorption and solubility. Dynamic mechanical analysis (DMA) was conducted to observe the trend in storage and loss modulus between the groups against temperature. Differences in the surface as a function of the post-polymerization conditions were qualitatively observed by scanning electron microscopy (SEM). The result shows that oxygen shielding during post-polymerization showed an increase in the degree of conversion (DC) and hardness of the resin surface. The highest DC was observed for GL group specimens at both room temperature and 80 °C. This result was confirmed by the SEM micrographs of the resin surface, where the interface between the layers of the GL group structure becomes more robust. However, a difference was observed between the samples prepared at room temperature and 80 °C. The flexural modulus was highest in the GL group, followed by the VA group, and lowest in the CON group at 80 °C. No difference in water absorption was observed for any groups, but high water solubility was observed in the GL group at room temperature. Overall, more significant differences in the properties were observed for the samples post-polymerized at 80 °C than at room temperature. The results of DMA analysis to determine the glass transition temperature showed a similar trend in all groups, and the storage modulus and loss rate obtained in the same experiment decreased in the order of GL, CON, and VA. In conclusion, an oxygen shielded post-polymerization environment at elevated temperature effectively improves the mechanical properties of photosensitive resin.

Finishing and Polishing of Composite Restoration: Assessment of Knowledge, Attitude and Practice Among Various Dental Professionals in India.

Aim The key to the success of a composite restoration lies in the important final step of finishing and polishing. This survey aims to assess the knowledge, attitude, and practice about finishing and polishing in composite restoration among various dental professionals in India. Materials and methods A cross-sectional questionnaire survey was conducted among various dental professionals in India. The participation of dentists was voluntary. A total of 350 responses were received, and the data were converted to Microsoft Excel 2019 program and descriptive statistics were analyzed using SPSS Version 21.0 software. Results Almost 99% of respondents know the importance of finishing and polishing procedures of composite restoration. Overall, 71% of respondents felt it is necessary to remove the surface layer to improve the surface characteristics of the composite restoration, 59.8% of professionals follow the sequential order of abrasives for finishing and polishing of composites, 74.2% use interproximal strips to finish interproximal areas of restoration, and 55.8% of professionals use polishing paste for the final polishing of composite restoration. Only 44.2% are aware of liquid polish/composite glaze, among which 12.4% of practitioners use liquid polish often. Conclusion Most of the respondents were aware of the benefits of proper finishing and polishing of composite restorations. However, still they need to follow proper sequential series of burs, abrasive points, disks, strips, and polishing pastes. The usage of surface sealants should be emphasized for enhanced results.

Laser Induced Thermal Effect on the Polymerization Behavior in Upconversion Particle Assisted Near-Infrared Photopolymerization.

Laser induced thermal effect is inevitable in upconversion particle assisted near-infrared polymerization (UCAP). Herein, the influence of thermal effects on the polymerization behavior are investigated. The effects of up-conversion particles content and NIR laser intensity on the polymerization rate and surface oxygen inhibition were systematically investigated, and the temperature evolution and complex viscosity changes in the polymerization system during the polymerization process were also monitored. In addition, polymerization experiments conducted on a controlled temperature platform were used to study the effect of NIR heating on the polymerization behavior. The results show that the near-infrared thermal effect promotes the polymerization reaction, but also causes severe oxygen inhibition which has an adverse effect on polymerization. Finally, NIR curing materials with enhanced mechanical properties than those of conventional UV curing materials were obtained.

Oxygen inhibition of surface composites and its correlation with degree of conversion and color stability

Abstract This study investigated the effects of oxygen inhibition and finishing/polishing procedures on the composite resin properties. One bulk-fill and two conventional composite resins (nanoparticle and microhybrid) were evaluated. Specimens were prepared using 4 surface treatments: control, no treatment; Gly, oxygen inhibition with glycerin; FP, finishing and polishing; Gly + FP, glycerin followed by finishing and polishing. The degree of conversion (DC) was measured using Fourier Transformed Infrared Spectroscopy (FTIR) immediately and after 15 days (n=5). Color stability (ΔEab, and ΔE00) and opacity were evaluated using a spectrophotometer after 15 days of immersion in coffee, using the CIELAB system (n=5). Data were analyzed by two-way ANOVA and Tukey tests (α=0.05) and opacity by two-way repeated-measures ANOVA. Glycerin usage increased significantly the DC however had no influence on the ΔEab, ΔE00 and, opacity values. Finishing and polishing reduced ΔEab and ΔE00 values, regardless of composite resins. Microhybrid showed higher opacity, followed by the nanoparticle and bulk fill, regardless of surface treatment. Post-polymerization polishing procedures resulted in lower conversion than using an oxygen inhibitor agent (Gly condition), but similar staining caused by coffee.

Resumo Este estudo investigou os efeitos da inibição de oxigênio e dos procedimentos de acabamento/polimento nas propriedades das resinas compostas. Foram avaliadas uma resina composta bulk fill e duas resinas convencionais (nanoparticulada e microhíbrida). Os espécimes foram confeccionados, variando o tratamento de superfície: controle, sem tratamento; glicerina (inibidor de oxigênio); acabamento e polimento; glicerina + acabamento e polimento. O grau de conversão (GC) foi medido pela Espectroscopia de Infravermelho Transformada de Fourier (FTIR) imediatamente e após 15 dias da confecção dos espécimes (n=5). Os índices de alteração de cor ΔEab, ΔE00 e opacidade foram avaliados por meio de espectrofotômetro, após 15 dias de imersão no café, utilizando o sistema CIELAB (n=5). Os dados da alteração da cor foram analisados pelos testes ANOVA de dois fatores e Tukey (α=0,05) e a opacidade por ANOVA de medidas repetidas. O uso de glicerina aumentou significativamente o GC, no entanto, não teve influência sobre os valores ΔEab e ΔE00. O acabamento e o polimento reduziram os valores de ΔEab e ΔE00, independentemente da resina composta. A resina microhíbrida apresentou maior opacidade, seguida pela nanoparticula e bulk-fill, independentemente do tratamento de superfície. O acabamento e polimento resultou em menor grau de conversão das resinas compostas se comparado ao uso de um agente inibidor de oxigênio (glicerina), porém apresenta resultados similares para a pigmentação pelo café.

[Curing method affecting the formation of oxygen inhibition layer on the surface of resin cement].

OBJECTIVE: To explore the conversion of resin monomer, the change of inorganic component and the influencing factors on the oxygen inhibition layer formed on the cured surface of resin cement. METHODS: Three kinds of resin cement were divided into three groups: (1) light-cured group: RelyX Veneer, NX3 (light-cured), Variolink N; (2) dual-cured group: RelyX U200 Automix, NX3 (dual-cured), Multilink Speed; (3) chemically-cured group, and the above 3 types of dual-cured resin cement cured without illumination could be used as chemically-cured resin cement. Each sample was provided with and without oxygen exposure of two matching surfaces, cured respectively, and the variables of light intensity and illumination time were set in the light-cured group and the dual-cured group. Scanning electron microscopy was used to observe the samples' surface morphology. Energy dispersive spectrometer was used to analyze the samples' composition of surface elements. Confocal Raman spectroscopy was used to measure the monomer conversion of resin cement and to obtain the thickness of the oxygen inhibition layer. RESULTS: (1) On the surface of cured resin cement, the weight percentage of oxygen element in the aerobic side was higher than that in the anaerobic side (P < 0.05), and the weight percentage of inorganic element was lower than that in the anaerobic side (P < 0.05). (2) The surface monomer conversion of the cured resin cement on the aerobic surface was significantly lower than that on the anaerobic surface (P < 0.05), and the surface monomer conversion on the aerobic surface and the anaerobic surface was the lowest in the chemically-cured group (P < 0.05), the dual-cured group was the highest (P < 0.05), and the light-cured group was between them. With the increase of light intensity or illumination time, the surface monomer conversion increased (P < 0.05). (3) The thickness of the oxygen inhibition layer was the thickest in the chemically-cured group [(40.27±2.81) µm](P < 0.05), the thinnest in the dual-cured group [(21.87±5.42) µm](P < 0.05) and light-cured group [(23.73±3.84) µm] was between them. With the increase of light intensity or illumination time, the thickness of the oxygen inhibition layer of resin cement decreased (P < 0.05). CONCLUSION: When resin cement is exposed to oxygen, it will form an oxygen inhibition layer, its surface's inorganic filler is less, the surface monomer conversion is lower. The surface monomer conversion and the thickness of oxygen inhibition layer are affected by curing mode and illumination factors.

A Simplified 2D Numerical Simulation of Photopolymerization Kinetics and Oxygen Diffusion-Reaction for the Continuous Liquid Interface Production (CLIP) System.

Additive manufacturing is a versatile technology for producing customized 3D products. In 2015, the Continuous Liquid Interface Production (CLIP) system was developed as a part of projection-type, UV-curable resin 3D printers. The CLIP system utilized the dead zone where oxygen inhibition occurs and prevents the UV-cured product from adhering to the UV illumination window. The CLIP system successfully produced complex shapes in a short time. This study investigated how the relationship between the photopolymerization rate, oxygen inhibition rate, and oxygen diffusion rate affects the shape of the product by means of a numerical simulation of the photopolymerization kinetics with oxygen diffusion and reaction. The results indicate that the vertical production speed and transmittance of UV light are crucial to controlling the conversion and shape precision of products.

A New Phosphine for Efficient Free Radical Polymerization under Air.

A new phosphine is proposed as efficient coinitiator for camphorquinone (CQ)-based photoinitiating systems for the free radical polymerization of (meth)acrylates. Remarkably, this new co-initiator can exhibit two functionalities: a phosphine moiety to overcome oxygen inhibition and an iodonium salt moiety as counter cation to initiate the polymerization process. Excellent polymerization performances in the presence of CQ for the free radical polymerization of methacrylates under blue light are observed, and amine-free systems can be easily developed from the proposed structure. The photopolymerization of composites is also investigated in the presence of the new phosphine (without iodonium counter cation) and very interesting depth of cure can be obtained from the new developed photoinitiating system after only 20 s of irradiation with a blue light-emitting diode.

Oxygen inhibition layer: A dilemma to be solved.

OBJECTIVE: This study aimed to evaluate the thickness of oxygen inhibition layer (OIL), produced on various composite materials, and to compare their interlayer shear bond strength (SBS), by treating the OIL with various agents. MATERIALS AND METHODS: The thickness of OIL of three different composite materials (120 specimens divided into three groups) Group 1 - Ivoclar Tetric N-Ceram (nanohybrid composite), Group 2 - Ivoclar Te Econom Plus (microhybrid composite), and Group 3 - GC EverX Posterior (a short glass fiber-reinforced composite) was evaluated. Each group was divided into four subgroups (A, B, C, and D) depending on the surface treatment given - no surface treatment (control group), ethanol, water spray, and grinding with SiC paper. This was followed by interlayer SBS testing. STATISTICAL ANALYSIS: The data were statistically analyzed using ANOVA at a significance level of P < 0.05. Tukey's post hoc analysis was performed following ANOVA to determine differences among the groups. RESULTS: The control group showed higher SBS irrespective of the type of composite material. The group treated with SiC paper resulted in the lowest interlayer SBS among all groups. Glass fiber composite showed higher interlayer SBS compared to both nanohybrid and microhybrid composites, irrespective of the surface treatment given. CONCLUSION: The OIL, which acts as an intermediate layer, is retained on the surface of the composite even after treatment with ethanol and water spray. The presence of an OIL improved the interlayer SBS of two adjacent composite layers and led to more durable adhesion. Rather, the absence of an OIL adversely affected the bond strength and led to adhesive interfacial failures.

Effect of Immediate Dentin Sealing on Polymerization of Elastomeric Materials: An Ex Vivo Randomized Controlled Trial.

STATEMENT OF PROBLEM: Interactions are suspected between resin coating and elastomeric impression material. PURPOSE: The purpose of this study was to identify possible interactions between two impression materials and resin-coated tooth surfaces. MATERIALS AND METHODS: Extracted molars (n = 10) underwent 1 of the 4 procedures: control group (unsealed tooth surface/impression); IDS group (immediate dentin sealing/impression); IDS/AB group (immediate dentin sealing/air blocking/impression); IDS/AB-P group (immediate dentin sealing/air blocking/pumicing/impression). Dentin bonding agents used were Adper single bond 2 and Clearfil SE bond. Impression materials used were Impregum Soft (polyether) and Aquasil (A silicone). A stereomicroscope was used to detect any residual impression material on the bonded tooth surface. RESULTS: The IDS group showed 100% faulty impressions. Air blocking the resin coating did not completely eliminate the oxygen-inhibited layer of Adper single bond 2. Clearfil SE Bond along with Aquasil generated ideal impressions in group IDS/AB, while all other combinations resulted in faulty impressions. The IDS/AB-P group yielded ideal impressions with Aquasil but generated faulty impressions with Impregum soft in most specimens. CONCLUSION: Immediate dentin sealing should be followed by air blocking and pumicing to generate ideal impressions with Aquasil (A silicone). Impregum Soft (polyether) is not recommended in combination with immediate dentin sealing. HOW TO CITE THIS ARTICLE: Khakiani MI, Kumar V, et al. Effect of Immediate Dentin Sealing on Polymerization of Elastomeric Materials: An Ex Vivo Randomized Controlled Trial. Int J Clin Pediatr Dent 2019;12(4):288-292.

Creating an Interface: Rendering a Double-Network Hydrogel Lubricious via Spontaneous Delamination.

Hydrogels engineered with specific surface chemistries and architectures have found myriad applications in electronics, biofouling, biolubrication, and biomedical devices. Free-radical polymerization is frequently employed to construct covalently bonded networks in hydrogels, and any inhibition of the radical reactions by oxygen at the surface of the reaction mixture is generally undesirable. The internal stress caused by the resulting gradient in the cross-linking density during polymerization can give rise to a physical deformation of the surface, resulting in wrinkles, creases, or cracks. However, this oxygen-inhibition effect can be positively utilized to create finely controlled surface structures. We describe a two-step cross-linking strategy for the fabrication of a P(AAm-AMPS)/alginate double-network hydrogel in the presence of air, which enables greater independent control over surface chemistry and functionality than homogeneously processed conventional double-network hydrogels. An alginate-rich "skin" layer is spontaneously delaminated due to the mechanical instability and osmotic mismatch between the swollen double-network hydrogel matrix and the rigid "skin" layer. Removal of the "skin" layer results in a lubricious surface with coefficients of friction as low as 0.02 against glass in aqueous solutions. The proposed strategy can be generalized to develop soft functional materials with unique structures and properties and precise control over the surface chemistry.

Universal Adhesives: Setting Characteristics and Reactivity with Dentin.

The aim of the study was to evaluate the performance of six commercially available universal dental adhesives: Adhese Universal (ADU), All-Bond Universal (ABU), Clearfil Universal Bond Quick (CBQ), G-Premio Bond (GPB), Prelude One (PRO) and Scotchbond Universal (SBU). The properties tested were: (a) degree of C=C conversion (DC%); (b) Vickers micro-hardness (VHN); (c) extent of oxygen inhibition (OI/µm), all related with the adhesive film properties; (d) extent of dentin demineralisation (DM%), insoluble salt formation (AS%); and (e) shear bond strength (SBS, self-etch mode) related to the adhesive-dentin interactions. Statistical analysis (α = 0.05) was performed by one-way ANOVA and Tukey's test (DC%, VHN, OI, DM% AS%) and Weibull analysis (SBS, σ0-ß). The DC ranged from 67.2-82.5% (all >GPB), OI from 5.6-18.6 µm (SBU > ADU, GPB, ABU > CBQ > PRO), microhardness from 1.1-6.6 VHN (SBU > ADU > ABU > CBQ > PRO > GPB: not measurable), DM from 69.3% (GPB) to 16-12.5% (CBQ, SBU, ADU) and 13.2-10.6% (ABU, ADU, PRO), in homogeneous groups and AS from 26-15.9% (ABU, CBQ > GPB, PRO, ADU, SBU). For SBS the σ0 (characteristic life) ranged from 29.3-16.6 MPa (CBQ, ADU, ABU, SBU > PRO > GPB), the ß (reliability) from 5.1-9.7 (p > 0.05). All failure modes were of mixed type (adhesive and composite cohesive). Although all these adhesives were based on the 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) adhesive monomer, the different co-monomers, solvents and catalysts led to variations in their film properties, reactivity and bonding capacity with dentin.

Raman spectroscopy as a tool to evaluate oxygen effects on the response of polymer gel dosimetry.

Currently, advanced dosimeters like polymer gels are capable of obtaining reliable and accurate 3D dose distributions from correlations with the different polymerization degrees induced by incident radiation. Samples of polymer gel dosimeters are commonly read out using magnetic resonance imaging or optical methods like visible light transmission or laser computed tomography. Alternatively, this work proposes and evaluates the implementation of Raman spectroscopy to provide direct information on the effect of oxygen permeating through the walls of phantoms on the polymerization initiated by irradiation in three types of polymer gel dosimeters, namely NIPAM, ITABIS and PAGAT. The aim of the present study is to provide better and complete interpretations using three different containers, adequate for integral, 2D and 3D dose mapping. Moreover, Raman spectroscopy has been used to analyze the well-known effect of oxygen inhibition on the different polymer gel dosimeters remarking the importance of avoiding air exposition during sample storage and readout. Dose-response curves for different polymer gels were obtained in terms of measurements with a calibrated ionization chamber. Additionally, dedicated Monte Carlo simulations were performed aimed at characterizing dose for different X-ray irradiation setups, providing also suitable information to evaluate oxygen diffusion through the sample wall. The obtained results were contrasted with optical transmission readout as well as Monte Carlo simulations attaining very good agreements for all dosimeter types.

Effect of Graphene Carbon Nitride on Ultraviolet-Curing Coatings.

Graphene carbon nitride (g-C3N4) was successfully prepared by semi-closed pyrolysis and then incorporated into the ultraviolet (UV)-curing system to synthesize different specimens of g-C3N4-hybridized UV-curing (g-C3N4/UV) coatings. The apparent appearance and dispersity g-C3N4 were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The influence of the curing speed and mechanical properties was also tested. The dispersion level of g-C3N4 can be kept less than 1 µm by mechanical mixing. The pencil hardness of composite coatings could be 6H while the adhesion based on glass could be 1 level. The degree of curing of the coating could be obviously improved by the addition of g-C3N4, leading to a 7 percent increase of the gel content. Additionally, the decomposition of hard segments of polyurethane acrylate could be avoided by the use of g-C3N4 resulting in an increasing stability to heat. We found the gel content in an aerobic environment was lower than that in an anaerobic environment. On this basis, the function and mechanism of g-C3N4 was investigated in detail and methods to eliminate the O2 were proposed.

Aerobic Conditions Enhance the Photocatalytic Stability of CdS/CdOx Quantum Dots.

Photocatalytic H2 production through water splitting represents an attractive route to generate a renewable fuel. These systems are typically limited to anaerobic conditions due to the inhibiting effects of O2 . Here, we report that sacrificial H2 evolution with CdS quantum dots does not necessarily suffer from O2 inhibition and can even be stabilised under aerobic conditions. The introduction of O2 prevents a key inactivation pathway of CdS (over-accumulation of metallic Cd and particle agglomeration) and thereby affords particles with higher stability. These findings represent a possibility to exploit the O2 reduction reaction to inhibit deactivation, rather than catalysis, offering a strategy to stabilise photocatalysts that suffer from similar degradation reactions.

Immobilization of Azospira sp. strain I13 by gel entrapment for mitigation of N2O from biological wastewater treatment plants: Biokinetic characterization and modeling.

Development of a strategy to mitigate nitrous oxide (N2O) emitted from biological sources is important in the nexus of wastewater treatment and greenhouse gas emission. To this end, immobilization of N2O-reducing bacteria as a biofilm has the potential to ameliorate oxygen (O2) inhibition of the metabolic activity of the bacteria. We demonstrated the effectiveness of calcium alginate gel entrapment of the nosZ clade II type N2O-reducing bacterium, Azospira sp. strain I13, in reducing levels of N2O, irrespective of the presence of O2. Azospira sp. strain I13 cells in the gel exhibited N2O reduction up to a maximum dissolved oxygen concentration of 100 µM in the bulk liquid. The maximum apparent N2O uptake rate, [Formula: see text] , by gel immobilization did not appreciably decrease, retaining 72% of the N2O reduction rate of the cell suspension of Azospira sp. strain I13. Whereas gel immobilization increased the apparent half-saturation constant for N2O, [Formula: see text] , and the apparent O2 inhibition constant, [Formula: see text] , representing the degree of O2 resistance, correspondingly increased. A mechanistic model introducing diffusion and the reactions of N2O consumption was used to describe the experimental observations. Incorporating Thieles modulus into the model determined an appropriate gel size to achieve N2O reduction even under aerobic conditions.