NaClO Concentration Research Articles

Depolymerization of Cellulose Components from Oil Palm Empty Fruit Bunches in Bleaching and Delignification Process

Oil palm empty fruit bunches (OPEFB) are oil palm industry waste which is indeed abundant. OPEFB waste has been explorated to make fiber, cellulose, and its derivatives. In the process of extracting cellulose, there is depolymerization of several components, both hemicellulose, lignin, color, and structural elements. The combination of bleaching under acidic conditions and alkaline delignification gave different changes, one of which depends on the type of bleacher, concentration, reaction time, and the number of stages carried out. This study aimed to examine the effect of NaClO2 concentration and bleaching time on the physical and chemical characteristics that indicate the depolymerization process of OPEFB fiber. Depolymerization can be indicated by changes in the cellulose color, the content of cellulose, and the changes in cellulose crystallinity. The change of cellulose mass was affected by the bleacher concentration and the bleaching time. High concentrations of bleacher will reduce the cellulose mass significantly. Similarly, the depolymerization of the chromophore elements in OPEFB fiber will show a change in color from brown to gray-white with different brightness intensities. The XRD test indicated that there was a correlation between low crystallinity with the use of high bleacher concentrations.

Dissolution of Ruthenium Metal by Combined Oxidizing and Reducing Action of Sodium Hypochlorite and HCl Solution

ABSTRACT Ruthenium (Ru) is an important platinum group metal for the manufacture of advanced materials owing to its chemical and physical properties. Generally, it is extremely difficult to dissolve Ru metal by using acidic solutions containing strong oxidizing agents. Therefore, pretreatments like alkali fusion roasting at high temperature are practiced to render the Ru metal soluble in aqueous solution. In this work, a simple procedure was proposed to dissolve Ru metal at room temperature without any pretreatments. The dissolution procedure consisted of two steps: (i) oxidation of Ru metal to RuO4 – by using pure NaClO solution; (ii) reduction of RuO4 – to stable Ru2OCl10 4– by using HCl as a reducing agent. The role of NaClO and HCl in the dissolution of Ru metal was discussed on the basis of the potential-pH diagram and the corresponding oxidation and reduction reactions. The effect of several parameters like the concentration of NaClO and HCl, temperature, time, and pulp density was investigated. Optimum conditions were obtained to completely dissolve Ru metal by using NaClO and HCl solution without alkali fusion.

Degradation of Polystyrene Nanoplastics in UV/NaClO and UV/PMS Systems: Insights into Degradation Efficiency, Mechanism, and Toxicity Evaluation

Nanoplastics have gradually become a concern due to the wide use of plastics. Nanoplastics in aqueous phase can be exposed to users through water supply networks and cannot be efficiently removed by conventional water treatment processes. This work studied the degradation of polystyrene nanoplastics (PS-NP) by two commonly used advanced oxidation systems: UV/NaClO and UV/peroxymonosulfate (PMS). Results showed that almost no turbidity was detected in the PS-NP solution (5.00 mg/L) after treated by both UV/NaClO and UV/PMS for 360 min, suggesting the excellent turbidity removal ability. Yet, scanning electron microscope (SEM) and total organic carbon (TOC) removal tests demonstrated that PS-NP could not be completely degraded by UV/NaClO. The mineralization rate using UV/NaClO was only 7.00% even when the NaClO concentration increased to 5.00 mM, and many PS-NP particles could still be observed in SEM images. By contrast, the mineralization rate reached 63.90% in the UV/PMS system under the identical experimental conditions, and no spherical particles appeared in the SEM results. Density functional theory (DFT) calculations revealed that the different reaction sites and energy barriers of SO4•− and •Cl on PS-NP resulted in the differences in mineralization rates and degradation intermediates. The degradation pathway of PS-NP by UV/NaClO and UV/PMS was proposed accordingly. Additionally, the intermediates toxicity evaluation by a luminescent bacteria test showed that the inhibition rate in the UV/NaClO system (2.97%) was not markedly different from that in the control group without any treatment (1.98%); while that in UV/PMS system increased sharply to 98.19%. This work demonstrated that UV/PMS was more effective in PS-NP degradation than UV/NaClO, and the chemical risks of degradation intermediates were non-negligible.

Suitable Methods of Inoculation and Quantification of Fusarium Root Rot in Lentil.

Lentil (Lens culinaris L. subsp. culinaris) is an important grain legume grown worldwide. As its popularity grows among consumers and more acres are produced, new root rot complexes have become more prevalent. This work sought to develop methods for studying root rot caused by Fusarium avenaceum in lentil using controlled environments. The objectives were to (i) find an effective and seed-safe sterilization technique, (ii) optimize the inoculation technique and lentil growing environment, and (iii) develop visual and automated disease scoring systems. Results showed the use of detergent and a low concentration (0.1%) of NaClO (the active ingredient in bleach) maintained germinability and effectively eliminated bacterial and fungal contamination on seeds. Other treatments, such as ethanol, reduced seed germination or failed to kill pathogenic fungi such as Fusarium spp. Placing inoculum at a moderate rate of 1 × 106 spores both directly on the seed and on top of the media covering the seed improved severity scores and reduced escapes compared with placement on top of the media only. Visual severity scoring systems and diagrammatic scales were developed for scoring the cotyledon region and roots. A computer vision algorithm was designed to improve the efficiency of scoring the cotyledon region and roots for disease severity using a simple RGB camera and lightbox. Visual and computer scores were best correlated when images were visually scored on a monitor, and multiple images were averaged. The scores generated from the computer vision algorithm had better correlations with visual scores for cotyledon rot (r = 0.92 and β1 = 0.96) than root rot (r = 0.62 and β1 = 0.67).

Application of Radial Type Multifiber Media Filtration Process for Combined Sewer Overflow Treatment

Fiber media filtration for combined sewer overflow (CSO) treatment was evaluated in this work. Pilot-scale experiments of CSO treatment involve seven layers that form radial-type fiber media filters. The fiber media filter was characterized using analysis techniques and exhibited extremely high hydrophobicity and negative charge. The results obtained for a sewer treatment plant at Tancheon in Seoul revealed potential for suspended solid, total organic carbon, and biochemical oxygen demand removal with efficiencies of 89.6%, 56%, and 42%, respectively. The results are consistent with the sieving effects and electrostatic repulsion between fiber media and pollutants. Head loss was induced by organic pollutants and was 10.5 cm after 20 h of operation. To mitigate the head loss induced by organic pollutants on the fiber media filter, sodium hypochlorite (NaClO) was used as a chemical backwashing agent. An NaClO concentration of 2000 mg/L with a soaking time of 24 h yielded an optimal head loss recovery of 96.2% of the initial head loss obtained for the virgin fiber media filter without media filter degradation. The result of the present study will provide practical insight and act as a technical guide for CSO treatment plant engineers.

A Novel Method Based on Hydrodynamic Cavitation for Improving Nitric Oxide Removal Performance of NaClO2.

In the removal of nitric oxide (NO) by sodium chlorite (NaClO2), the NaClO2 concentration is usually increased, and an alkaline absorbent is added to improve the NO removal efficiency. However, this increases the cost of denitrification. This study is the first to use hydrodynamic cavitation (HC) combined with NaClO2 for wet denitrification. Under optimal experimental conditions, when 3.0 L of NaClO2 with a concentration of 1.00 mmol/L was used to treat NO (concentration: 1000 ppmv and flow rate: 1.0 L/min), 100% of nitrogen oxides (NOx) could be removed in 8.22 min. Furthermore, the NO removal efficiency remained at 100% over the next 6.92 min. Furthermore, the formation of ClO2 by NaClO2 is affected by pH. The initial NOx removal efficiency was 84.8-54.8% for initial pH = 4.00-7.00. The initial NOx removal efficiency increases as the initial pH decreases. When the initial pH was 3.50, the initial NOx removal efficiency reached 100% under the synergistic effect of HC. Therefore, this method enhances the oxidation capacity of NaClO2 through HC, realizes high-efficiency denitrification with low NaClO2 concentration (1.00 mmol/L), and has better practicability for the treatment of NOx from ships.

High-Yield Alpha-Cellulose from Oil Palm Empty Fruit Bunches by Optimizing Thermochemical Delignification Processes for Use as Microcrystalline Cellulose.

Oil palm empty fruit bunches (OPEFB) are lignocellulosic materials that are a by-product of the palm oil industry, which have less use and utilization is still limited. OPEFB's high cellulose content could potentially develop into various bioproducts, especially biomaterials. The thermochemical delignification process can obtain high-yieldalpha-cellulose. The cellulose extraction process can be done by combining the bleaching process under acidic conditions and alkaline delignification to obtain high-purity cellulose. The bleaching conditions vary in the concentration of NaClO2, the length of bleaching, the temperature, and the number of stages. The research obtains high α-cellulose by optimizing bleaching conditions under acidic conditions in cellulose's OPEFB extraction with variability on NaClO2 concentration and bleaching time using response surface methodology (RSM). The bleaching process was implemented at an early stage with a concentration of 3% NaClO2 and a bleaching time of 2 hours as a center point with a bleaching cycle of twice at pH 4-4.5 using acetic acid. Bleached fibers were delignified using 10% NaOH for 2 hours at room temperature. The RSM analysis resulted in optimum bleaching conditions at a concentration of 3.22% NaClO2 for 1 hour, yielding OPEFB's cellulose of 82.96% ± 2.53, hemicellulose of 9.27% ± 2.28, and lignin of 1.68% ± 0.58. The validation and verification process in the bleaching conditions obtained cellulose of 84.87% and α-cellulose of 88.51%, with a crystallinity index of 70.55% and crystallite size of 2.35 nm. Scanning electron microscopy on surface cellulose morphology at optimum bleaching helped remove hemicellulose impurities, lignin, and inorganic materials and a more intensive opening of cellulose fibrils. The bleaching process optimization point was verified to improve the delignification performance and potentially produce high yield α-cellulose content for microcrystalline cellulose use.

Chlorine resistant polyamide desalination membrane prepared via organic-organic interfacial polymerization

Desalination of seawater, brackish water and urban sewage is an important way to solve the global water shortage. Polyamide (PA) membranes, including reverse osmosis (RO) membrane and nanofiltration (NF) membrane, are the primary technology for seawater desalination and clean water production. However, traditional thin-film composite PA (TFC-PA) membranes prepared from interfacial polymerization (IP) of amine monomers (either piperazine or m-phenylenediamine) in water and acyl chloride monomers in organic solvent are incapable of tolerating strong acid and chlorine environment. Here, we develop a new IP process, which takes place at the immiscible interface between dimethylacetamide (DMAc) and hexane (referred to as organic/organic IP), to prepare both chlorine-resistant and acid-resistant TFC-PA membranes. Compared to conventional water/oil IP process, the organic/organic IP process can adapt more kinds of amine monomers rather than just PIP, such as tetra (4-aminophenyl) methane (TMAP), tris (4-aminophenyl) amine (TAPA), and 4,4′,4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine (TTA), which we studied in this work, thereby extending the PA molecular structure and enabling the membranes with greatly improved chemical stability. Among them, the TAPM-based TFC-PA membrane exhibits a NaCl rejection of 95.9% and no obvious NaCl rejection deterioration after soaking in a high concentration of NaClO (1000 ppm, pH 7) for more than 30 h, indicating excellent chlorine resistance. The TTA-based TFC-PA membrane shows a Na2SO4 rejection of 97% and remains unchanged after being exposed to a wide pH scan of 2–12. The Organic/organic IP provides a new and easy-to-operate platform for designing chlorine and acid resistant TFC-PA membranes, which will greatly improve their environmental stability as the most advanced desalination membrane at present.

Tuning the properties of pineapple peel cellulose nanofibrils by TEMPO-mediated oxidation and ball milling

In this study, the oxidized cellulose nanofibrils from pineapple peel (PP-TOCNF) were prepared by TEMPO-mediated oxidation followed by ball milling. The influence of oxidation degree on the structure and properties of PP-TOCNF were investigated, including Fourier transform infrared spectroscopy , X-ray diffraction, atomic force microscope (AFM), X-ray photoelectron spectroscopy and thermogravimetry, as well as the potential application in aerogels. The results suggested that TEMPO oxidation facilitated the dispersion of PP-TOCNF due to the strong electrostatic repulsion between –COO− groups. Regulating oxidation degree by varying NaClO concentration could effectively adjust the –COO− content (0.167–0.550 mmol/g), zeta potential (− 18 to − 34 mV) and rheological properties. The obtained PP-TOCNF showed a long fibrillar structure, whose average diameter and CrI values gradually decreased with the increase of oxidation degree. The PP-TOCNF-based aerogels exhibited a light weight, good porosity, water absorption, and mechanical properties, which also can be easily adjusted by oxidation degree of PP-TOCNF. Furthermore, TEMPO oxidation improved the stability and shape recovery ability of aerogels in water.Graphical abstract

Enhancement Effects of Water Magnetization and/or Disinfection by Sodium Hypochlorite on Secondary Slaughterhouse Wastewater Effluent Quality and Disinfection By-Products

Wastewater disinfection is one of the most critical issues in protecting human health against exposure to waterborne pathogenies. Chlorine is among the most commonly used disinfectants in many wastewaters’ treatment plants. Nevertheless, disquiets regarding chlorine’s disinfection by-products (DBPs) have grown recently. One of the most effective ways to reduce DBPs generation is to reduce chlorine dosage by increasing disinfectant efficiency. Using magnetic field (MF) in wastewater treatment is one of the promising research topics with significant progression. This study aimed to evaluate the efficiency of using a magnetic field and/or sodium hypochlorite (NaClO) disinfection on secondary slaughterhouse wastewater effluent quality and by-products. Three groups of secondary slaughterhouse wastewater effluents were used: G1 was treated with NaClO only at 0, 2, 4, and 6 mg/L; G2 was treated with exposure to MF at 14,500 gausses, and G3 was pretreated with MF, then NaClO at the exact chlorine dosages and MF strength. The results showed an augmented effect when using a magnetic field as a pre-treatment step before NaClO treatment in the remediation of slaughterhouse wastewater over the use of any of them solely. The removal rate of COD and BOD increased by up to 26 and 20%, respectively, when pre-treatment with MF was employed as a mean percentage at all chlorine dosages, while TSS, TDS, and EC increased by 23.5 and 5.5%, respectively. Over and above, the removal rate for each TN and TP increased by 12 and 6.5% as a mean percentage at all chlorine dosages when using a combination of the two. In addition, pre-treatment by MF reduced the required concentration of NaClO from 6 to 4 mg/L, resulting in an 11% increase in the reduction rate of total coliform count, 8% increase in the reduction rate of fecal coliforms, and 10% increase in the reduction rate of E. coli and 5% in Salmonella via increasing the disinfection efficiency of NaClO. Finally, it decreased the concentration of Chloroform produced by more than 77.2% by using the higher concentration of NaClO (6 mg/L). The issue that approved the promising approach of using MF as a pre-treatment step in the treatment of slaughterhouse wastewater provides the advantage of using smaller dosages of disinfection, lowering the cost of the procedure process, and reducing the harmful concentration of DBPs.

CFDA-AM staining to assess the metabolic activity of Giardia duodenalis cysts inactivated by chlorine, boiling and ultraviolet irradiation.

Giardia duodenalis is responsible for several waterborne gastrointestinal outbreaks worldwide. In addition to limitations presented by the main disinfection methods, assessing the inactivation efficiency of cysts after the treatment also poses challenges. Thus, this study aimed to use the 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) staining protocol to evaluate the viability of G. duodenalis cysts inactivated by different UV and chlorination doses and boiling times. Under epifluorescent microscopy, metabolically active cysts that presented green fluorescence were considered viable. In contrast, when no green fluorescence could be observed, organisms were considered non-viable. Although statistical analysis revealed that increasing the UV dose did not significantly decrease the percentage of viable cysts, the fluorescence signal intensity decreased considerably when the cysts were irradiated with a dose equal to or greater than 80 mJ cm-2. Regarding chlorination and boiling treatments, this study demonstrated that no cyst showed fluorescence at the lowest NaClO concentration (0.5 mg/L) and in the shortest boiling time (2 min). Despite some limitations regarding the use of metabolic activity as a viability marker, this methodology is rapid, easy to run and cost-effective. Thus, we conclude that the CFDA-AM staining protocol has the potential to be used to assess Giardia cyst inactivation, although further research is required.

Degradation of iopamidol by UV365/NaClO: Roles of reactive species, degradation mechanism, and toxicology

The degradation of iopamidol (IPM) was investigated using a UV365/NaClO system. The reactive species (HO·, ClO·, ozone, Cl·, and Cl2−·) in the system were identified, and the changing trends of the percentage contributions of these reactive species to IPM removal under various conditions were systematically evaluated. The results showed that ClO· and HO· played the most significant roles in the apparent pseudo-first-order rate constants of IPM degradation (kobs, min−1) in the control experiment, and their percentage contributions to kobs were 41.31% and 34.45%, respectively. In addition, Cl· and Cl2−· together contributed 22% to the kobs. Furthermore, the contribution of ozone to the IPM removal could be neglected. The concentrations of these species increased significantly when the concentration of NaClO was increased from 50 µM to 200 µM, while the percentage contribution of ClO· to kobs was greatly increased. The concentrations and percentage contributions of HO· and ClO· decreased significantly as the solution pH increased from 5 to 9, with Cl2−· playing a greater role in the degradation of IPM under alkaline conditions. While Cl− or HCO3−/CO32− significantly promoted the generation of Cl2−· or CO3−·, neither had an obvious effect on kobs, suggesting that Cl2−· and CO3−· should have a certain reactivity with IPM. Compared with that of Cl2−·, the percentage contribution of ClO· and Cl· to kobs was more likely to be inhibited by NOM. In addition, the organic and inorganic oxidation products of IPM were detected. The oxidation mechanisms of IPM degradation in the UV365/NaClO system, such as the H-extraction reaction, deiodination, substitution reaction, amide hydrolysis, and amine oxidation, were proposed according to the obtained 15 organic products. No effect on acute toxicity towards Vibrio fischeri and Photobacterium phosphoreum was detected during the oxidation of IPM by the UV365/NaClO system. Furthermore, the engineering feasibility of the oxidation system was demonstrated, by the effective degradation of IPM in actual water. However, HOI rapidly accumulated during the removal of IPM in the UV365/NaClO system, which poses certain environmental risks and will needs to be investigated.

Comparative evaluation of chlorous acid and sodium hypochlorite activity against SARS-CoV-2.

A novel coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), suddenly emerged in China in 2019, spread globally and caused the present COVID-19 pandemic. Therefore, to mitigate SARS-CoV-2 infection effective measures are essential. Chlorous acid (HClO2) has been shown to be an effective antimicrobial agent. However, at present there is no experimental evidence showing that HClO2 can inactivate SARS-CoV-2. Therefore, in this study, we examined the potential of HClO2 to inactivate SARS-CoV-2 in presence or absence of organic matter and the results were compared with that of sodium hypochlorite (NaClO), another potent antimicrobial agent. When concentrated SARS-CoV-2 was incubated with 10 ppm HClO2 for 10 s, viral titre was decreased by 5 log of 50% tissue culture infective dose per mL (TCID50 ml−1). However, the same concentration of NaClO could not inactivate SARS-CoV-2 as effectively as HClO2 did even after incubation for 3 min. Furthermore, 10 ppm HClO2 also inactivated more than 4.0 log of TCID50 within 10 s in the presence of 5 % fetal bovine serum used as mixed organic matters. Our results obtained with HClO2 are more effective against SARS-CoV-2 as compared to NaClO that can be used for disinfectant against SARS-CoV-2 .

Overhauling the Effect of Surface Sterilization on Analysis of Endophytes in Tea Plants

Increasing evidence shows that plant Endophytes play a crucial role in the fitness and productivity of hosts. Surface sterilization is an indispensable process before high-throughput sequencing (HTS) and tissue separation of plant endophytes, but its potential impact on the composition and diversity of endophytes has rarely been investigated. In the present work, the influence of sodium hypochlorite (NaClO) on the diversity of endophytic bacteria and fungi in leaves and stems of tea plants was investigated. We found that the diversity of bacterial endophytes was significantly affected by the concentration of NaClO as well as the pretreatment time. Pretreatment with 0.5% NaClO for 8 min and 2.0% NaClO for 3 min were suitable for the tea plant leaves and stems, respectively, but the effects of NaClO on the diversity of fungal endophytes were limited according to the results from HTS. Regardless of NaClO sterilization, most of the endophytes in tissues, such as the dominant taxa, could not be Isolated by using the regular culture-dependent approaches. Collectively, our results demonstrated that the pretreatment with NaClO should be modified to precisely understand the diversity of endophytes from different tissues of tea plants and also indicate that more attention should be paid to establish specific culture-dependent protocols for the isolation of plant endophytes.

Influence of Chlorine Oxyacid on the Electrooxidation of Methanol in Strong Acid

An electrochemical oxidation of methanol in a strong acid solution was investigated at a polycrystalline platinum electrode in the presence of different concentrations of hypochlorite. The addition of a slight amount of hypochlorite brought about drastic increase in the oxidation current of methanol, because the presence of hypochlorite inhibited the formation of a platinum oxide film on platinum electrodes. However, the oxidation current of methanol decreased with increasing the concentration of coexisting hypochlorite. The result may be due to i) the enhancement of the methanol adsorption to the surface of platinum electrodes by the inhibition of the formation of oxide film, and ii) the inhibition of methanol adsorption on platinum electrodes by higher concentration of NaClO and chemical compounds generated by the chemical reaction between methanol and increased hypochlorite.

Effects of sodium hypochlorite treatment on the chlorophyll fluorescence in photosystem II of microalgae

Chlorophyll fluorescence-based method shows great potentials for on-site assessing the vitality of algae in treated ship's ballast water. However, there is very limited information on the mechanism of chlorophyll fluorescence in photosystem II (PSII) after the NaClO treatment. In this paper, the effects of NaClO treatments with five concentrations (0.01, 0.04, 0.08, 0.12 and 0.15 mg/L) and treating periods (6, 24 and 48 h) on the chlorophyll fluorescence kinetics and spectra of Chlorella vulgaris (C. vulgaris) and Platymonas helgolandica (P. helgolandica) were investigated. Experimental results showed that both exposure time and dose were important factors that affect the toxicity of NaClO to microalgae. Further analyses showed that the maximum photochemical quantum yield of PSII, photochemical quenching and yield decreased rapidly with the increase in NaClO concentrations in the range of 0.04 mg/L to 0.15 mg/L, suggesting that NaClO seriously inhibited PSII reaction centers of algae. In addition, the maxima value of fluorescence at excitation wavelength still appeared near 437 nm and 468 nm under NaClO stress, pointing to the pigments for fluorescence produced by algae were mainly chlorophyll a and chlorophyll b antenna. As compared to chlorophyll a, the relative fluorescence intensity of chlorophyll b decreased significantly in the all of NaClO treatments. According to the fluorescence emission spectra, treatment of NaClO resulted in a shift of the maximum peak of C. vulgaris and P. helgolandica from 685.2 nm to 681.9 nm and 685.2 nm to 680.5 within 6 h, respectively. This indicates that the structure of antenna light-absorbing pigments of PSII changed under NaClO stress. These results revealed that the chlorophyll fluorescence mechanism in PSII of damaged microalgae occurred variation, which was important for the reliable application of on-site analysis of ballast water indicator based on chlorophyll fluorescence detection.

Sodium hypochlorite induced inhibition in anaerobic digestion and possible approach to maintain methane fermentation performance

Since sodium hypochlorite (NaClO), a commonly used chemical to deal with membrane fouling, is toxic to microorganisms, it is a major concern in the membrane cleaning process. In this study, the concentration-dependent effects of NaClO (0–9 g/L) on the biodegradation performance and microbial activity were investigated via batch experiments. The methane production (obtained approximately 140 mL) and microbial community revealed by principal coordinates analysis were almost unaffected when the NaClO concentration ranged between 0 and 3 g/L. A follow-up batch experiment was conducted and revealed that the microbial products could help protect or recover the activity of anaerobic microorganisms at a high NaClO concentration of 10 g/L. Additionally, correlation analysis was used to investigate the associations between the 15 major bacterial genera. Moreover, the microbial analysis results indicated that the top 10 operational taxonomic units most affected by NaClO were primarily coryneform and filamentous bacteria.

Visible light-induced photocatalytic chlorine activation enhanced the 0.5% neutral-NaClO/TiO2-x system as an efficient and safe root canal irrigant

A root canal irrigant system with efficiency and safety was constructed using TiO 2-x nanoparticles, 0.5% Neutral-NaClO, and visible light irradiation, generating extensive ROS and RCS rapidly via photocatalysis chlorine activation process. The process enhanced the antibacterial and tissue-dissolution abilities of low concentrations of NaClO in endodontic therapy. • A novel 0.5%Neu-NaClO/TiO 2-x root canal irrigant system was proposed. • The photocatalysis chlorine activation boosted the production of ROS and RCS. • The system exhibited strong antibacterial and tissue-dissolving abilities. • The system showed acceptable application safety in vivo. Root canal irrigation is an essential step for ensuring successful root canal therapy (RCT). Among available irrigants, sodium hypochlorite (NaClO) (0.5%-5.25%) is the most used irrigant solution because of its comprehensive ability to kill bacteria and dissolve organic tissues. Hence, high concentration of NaClO may have negative effects that would lead to devastating complications, and low concentration of NaOCl is safe but shows decreased efficacy. Therefore, a safe and efficient novel catalysis-enhanced root canal irrigant system consisting of 0.5% neutral-NaClO (pH = 7.5), TiO 2-x nanoparticles (5 mg mL −1 ), and visible light irradiation (LED, 10 W, 405–800 nm) was proposed. The effect of the photocatalytic chlorine activation rapidly increased the generation of reactive oxygen species (ROS, •OH) and reactive chlorine species (RCS, •Cl and •ClO) in the system. Consequently, the system exhibited greatly enhanced degradation ability toward methylene blue and typical biological macromolecules, implying its good antibacterial and tissue dissolution activities. Additionally, the antibacterial rates against Enterococcus faecalis in both planktonic and biofilm forms were > 99% after treatment with the proposed system for 5 min, which was comparable to that of the 3% alkaline NaClO. Meanwhile, the system showed desirable pulp tissue-dissolving efficacy, successfully solving the dilemma caused by neutralization. L929 cell experiments as well as rats subcutaneous injection experiments demonstrated the biocompatibility and safety of the system. This work describes a safe and effective endodontic irrigant and proposes a promising strategy for developing NaClO-based disinfectants for wider application.

Assessment of the antimicrobial effects of sodium hypochlorite on Enterococcus faecalis by D2O-labeled single-cell Raman micro-spectroscopy.

To systematically evaluate the feasibility of D2O-labeled single-cell Raman micro-spectroscopy in drug resistance research and test the susceptibility of Enterococcus faecalis (E. faecalis)to sodium hypochlorite. 1) The growth of E. faecalis in different doses of D2O and the regularity of D2O intake were evaluated through absorbance measurement and D2O-labeled single-cell Raman micro-spectroscopy to examine the universality of D2O-labeled single-cell Raman micro-spectroscopy in bacterial resistance research. 2) Broth dilution method and absorbance measurement were performed to determine the minimum inhibitory concentration (MIC) of NaClO against E. faecalis and the MIC based on metabolic activity (MIC-MA) in vitro via D2O-labeled single-cell raman micro-spectroscopy. 1) The growth of E. faecalis was not significantly inhibited by ≤40% D2O in the medium. E. faecalis could actively metabolize D2O and exhibit a C-D ratio in specific areas of Raman micro-spectroscopy results. The C-D ratio of E. faecalis at the stationary phase was positively correlated with D2O concentration. 2) The MIC and MIC-MA of NaClO against E. faecalis were 0.45 and 0.9 g·L-1, respectively. The concentration of MIC-MA was twice that of MIC. D2O-labeled single-cell Raman micro-spectroscopy is important in screening antimicrobial agents and evaluating the efficacy of antimicrobial agents. It is suitable for evaluating the effect of drugs on bacterial metabolic activities. NaClO showed an effective antimicrobial activity against E. faecalis. E. faecalis ceased propagation yet remained highly metabolically active when it was exposed to NaClO at the MIC level. The metabolic activity of most cells was inhibited only when they were exposed to NaClO at the MIC-MA level.

Preparation of antimicrobial poly (ethylene-co-vinyl alcohol) membrane by grafting with N-halamine

5,5-dimethyl-3-(3′-triethoxysilylpropyl)-hydantoin (SPH) was grafted and chlorinated on the surface of poly (ethylene-co-vinyl alcohol) (EVOH) membrane. The effects of modification method, reaction time, N-halamine amount, reaction temperature and NaClO concentration on the chlorine content and antibacterial activity of N-halamine modified EVOH membrane were investigated. It was found that, submerge reaction was more effective than the dip-coating reaction in the modification of EVOH membrane. Under the same conditions, the chlorine content of the membrane prepared by the submerge reaction is 1.8 times that of dip-coating reaction. With the increased grafting time, the chlorine content of EVOH membrane showed an obvious rising trend from 0.025% to 0.037%. With the increase of NaClO concentration, the chlorine content rose from 0.010% to 0.037%. For the E. coli concentration of 1.86 × 106 CFU/mL, with the rising chlorine content (0.025% - 0.037%), the inactivation rate of EVOH membrane increased significantly (72% - 100%). The N-halamine modified EVOH membranes showed excellent regeneration and reusability performance, indicating great potential in the applications.