Sodium Hypophosphate Research Articles

Synthesis of Ni, Cu plated nano-Al2O3 composite powders and autocatalytic mechanism

This research proposes a novel method that combines sodium hypophosphite reduction, Ni re-activation, and electroless copper plating to fabricate pure Cu-Ni/Nano-Al2O3 composite powder. The research investigated the effects of the re-activator on the characteristics of Cu-Ni/Nano-Al2O3 composite powders and the autocatalytic mechanism of electroless copper plating on the nano-alumina surface under two re-activation conditions. The results showed that the method successfully eliminates Cu2O and improves the efficiency of electroless copper plating. During electroless copper plating, when Ni2+ is used as the re-activator, sodium hypophosphate only releases one electron and one active hydrogen, thus it cannot completely reduce the Cu2+. However, when nickel is used as the re-activator, sodium hypophosphite can release active hydrogen in two steps and reduce the Cu2+ to Cu. The purification strategy proposed, and the relationship between the electroless plating process and the autocatalytic activity of metals are highly valuable for manufacturing metal matrix composites in special applications.

Synthesis of β-Hydroxyhydrophosphonic Acids from Inorganic Sodium Hypophosphite

AbstractAn efficient approach to access β-hydroxyhydrophosphonic acid derivatives is reported by ring-opening reaction of readily available epoxides with green, inexpensive, and safe inorganic salt sodium hypophosphate as the phosphorus source in the presence of silver trifluoromethanesulfonate as the catalyst. The reaction is achieved under simple operation and exhibits excellent selectivity as well as good functional group compatibility.

Flat Absorber Black PEO coatings on Ti6Al4V for spacecraft thermal control application

Black appearance and flat absorber, i.e., high solar absorptance (αs) and high IR emittance (εir) surfaces, are essential for optical benches and optical mounts in astronomical and scientific payloads/spacecraft. Generally, these optical benches and optical mounts are fabricated by Ti6Al4V alloy due to its superior mechanical and thermal properties. However, bare Ti6Al4V is restricted for spacecraft thermal control applications due to its low emittance, intermediate absorptance, and moderate corrosion resistance behaviors. Hence, plasma electrolytic oxidation (PEO) technique was utilized to develop black and flat absorber coatings on bare Ti6Al4V alloy. Sodium silicate (SS), sodium hypophosphate (SHP), and potassium fluoride (KF) were used for the preparation of the electrolytic bath. Process parameters such as current density, duty cycle, frequency, the concentration of electrolytes, and duration were judiciously altered to get uniform PEO coatings with the flat absorbing property. Six numbers of PEO coatings were finally chosen for further in-depth characterizations as they showed adequate flat absorbing property. The phase composition, microstructure, roughness, and wettability of those PEO coatings were thoroughly studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), profilometry, and water contact angle measuring techniques, respectively. Thermo-optical properties viz., εir and αs of the coatings were recorded by portable IR emissometer and solar reflectometer, respectively, and electrical sheet resistance was measured by two probe method. The Nanomechanical properties of the coatings, such as modulus (E) and nanohardness (H), were evaluated by the nanoindentation technique. The PEO coatings were also investigated with respect to potentiodynamic polarization to investigate corrosion resistance of the PEO coatings. The highest εir value of PEO coating was achieved as 0.87 for a 20% duty cycle with a combination of SS + SHP electrolytes, while the maximum αs value was achieved as 0.83 for the same 20% duty cycle with a combination of SS + SHP + KF electrolytes.

The surface functional modification of Ti3C2Tx MXene by phosphorus doping and its application in quasi-solid state flexible supercapacitor

The surface modification of MXene by heterogeneous atoms shows great potential in improving the charge storage capacity of MXene. Herein, a strategy of rapid in-situ phosphorus doping at low temperature is demonstrated for preparing functionalized Ti3C2Tx MXene (Ti3C2Tx-P) using sodium hypophosphate as phosphorus source. The phosphorus doping can increase the layer spacing of Ti3C2Tx and yield PO and PC bonds in Ti3C2Tx, resulting in more rapid paths for the migration of electrolyte ions into electrode and more active sites for pseudocapacitance effects. As flexible electrode of supercapacitor, the specific capacitance of Ti3C2Tx-P reaches as high as 476.9F g−1 (745.4F cm−3), which is far larger than that of the raw Ti3C2Tx (344.4F g−1, 438.5F cm−3). In addition, a flexible quasi-solid supercapacitor device assembled by Ti3C2Tx-P film shows high specific capacitance of 103F g−1 at 5 mV s−1. When the power density is 250 W kg−1 and 10000 W kg−1, the corresponding energy density reaches 15.8 Wh kg−1 and 6.1 Wh kg−1, respectively. Therefore, our work not only reveals the role of P atom doping in improving the structure, composition and electrochemical performance of Ti3C2Tx, but provides a method for surface modification and functionalization of MXene materials.

In Situ Synthesis of Copper Nanoparticles on Dielectric Barrier Discharge Plasma-Treated Polyester Fabrics at Different Reaction pHs.

Polyester (PET) fabrics are widely applied in functional textiles due to their outstanding properties such as high strength, dimensional stability, high melting point, low cost, recyclability, and flexibility. Nevertheless, the lack of polar groups in the PET structure makes its coloration and functionalization difficult. The present work reports the one-step in situ synthesis of copper nanoparticles (CuNPs) onto the PET fabric employing sodium hypophosphate and ascorbic acid as reducing and stabilizing agents, at acidic (pH 2) and alkaline pH (pH 11). This synthesis (i) used safer reagents when compared with traditional chemicals for CuNP production, (ii) was performed at a moderate temperature (85 °C), and (iii) used no protective inert gas. The dielectric barrier discharge (DBD) plasma was used as an environmentally friendly method for the surface functionalization of PET to enhance the adhesion of CuNPs. The size of the CuNPs in an alkaline reaction (76-156 nm for not treated and 93.4-123 nm for DBD plasma-treated samples) was found to be smaller than their size in acidic media (118-310 nm for not treated and 249-500 nm for DBD plasma-treated samples), where the DBD plasma treatment promoted some agglomeration. In acidic medium, metallic copper was obtained, and a reddish color became noticeable in the textile. In alkaline medium, copper(I) oxide (Cu2O) was detected, and the PET samples exhibited a yellow color. The PET samples with CuNPs presented improved ultraviolet protection factor values. Finally, a minimal concentration of copper salt was studied to obtain the optimized antibacterial effect against Staphylococcus aureus and Escherichia coli. The functionalized samples showed strong antibacterial efficacy using low-concentration solutions in the in situ synthesis (2.0 mM of copper salt) and even after five washing cycles. The DBD plasma treatment improved the antibacterial action of the samples prepared in the alkaline medium.

Influence of Citric Acid on the Bond Strength of Beech Wood.

In this study, beech wood (Fagus silvatica L.) has been chemically modified with citric acid (Acidum citricum) and sodium hypophosphate (SHP) as the catalyst and gradually thermo-condensed in the dryer. Afterwards, wetting angle, surface energy, and shear strength of glued joints of modified and unmodified wood were determined. Testing of the bond strength according to standard EN 204 and comparison between modified and unmodified samples were executed. The adhesive used for bonding samples was polyvinyl acetate (PVAC), commonly used for gluing solid wood panels. Testing material was divided into three groups (dry, wet, and wet conditioned samples), within which statistical analysis was performed, and the significance of the differences between the modified and unmodified samples was determined. Surface energy is correlated with the bond strength, indicating that modification with citric acid negatively affects the adhesive properties of beech wood. A reduction in the bond strength of modified wood glued with PVAC glue compared to unmodified wood was determined. All the results indicate that the modified samples do not meet the minimum requirements for EN 204 bonded with PVAC glue. Therefore, it will be necessary to conduct further studies using other types of adhesives to investigate whether modified wood might be suitable for gluing.

Development and Characterization of High Emittance and Low-Thickness Plasma Electrolytic Oxidation Coating on Ti6Al4V for Spacecraft Application

Plasma electrolytic oxidation (PEO) or microarc oxidation process has been carried out on Ti6Al4V substrate in electrolytic bath containing sodium silicate and sodium hypophosphate. The phase composition, microstructure and roughness of the PEO coating are examined by x-ray diffraction, scanning electron microscopy and profilometry techniques, respectively. Wavelength-dependent thermo-optical properties viz. solar absorptance ( $$\alpha_{s}$$ ) and IR emittance (eir) are recorded by UV-VIS-NIR and FTIR spectrophotometer, respectively. Nanomechanical properties such as nanohardness (H) and Young’s modulus (E) are evaluated by well-established nanoindentation technique. The PEO coating is found to be hydrophobic (contact angle ~108°) and possesses low thickness of 5-9 $$\upmu$$ m. Average eir is obtained to be 85% while average $$\alpha_{s}$$ is recorded as 76%. The characteristics H and E values are 2.59 GPa and 81.45 GPa, respectively. The PEO coating is also characterized with respect to potentiodynamic polarization and impedance spectroscopy to evaluate corrosion resistance. The total impedance and corrosion current density (icorr) are in the order of 1 MΩ and 10-8 µA.cm-2, respectively. The results indicate superior corrosion resistance of the present PEO coating compared to similar coatings reported in the literature.

Comprehensive recovery of arsenic and antimony from arsenic-rich copper smelter dust

In view of reducing contaminant and recovery arsenic and antimony, a novel technology was proposed to recover arsenic and antimony from arsenic-rich copper smelter dust comprehensively. The technique route includes three stages: arsenic and antimony trioxides were leached from the copper smelter dust with hydrochloric acid; trivalent arsenic ions (As3+) were then reduced to less toxic simple arsenic (As) by sodium hypophosphate (NaH2PO2) and recovered; and stepwise recovery of antimony by SbCl3 was achieved by the continuous distillation technique. The results indicates that the leaching efficiency of As and Sb was over 97.5% and 96.8% under conditions of initial 4.0 mol/L HCl, liquid-solid ratio (L/S) of 6:1, leaching temperature of 363 K and time of 2 h. Over 92.5% arsenic was recovered by NaH2PO2 reduction under the suitable conditions: 363 K, 1.5 h and 2.0 times addition of NaH2PO2. The recovery rate of Sb is more than 97.53% at 393 K. The distillation temperature of SbCl3 was optimized between 463 K and 473 K. The corresponding mechanisms of the leaching and recovering of arsenic and antimony were systematically investigated and confirmed by E-pH diagram, thermodynamic calculation, arsenic speciation, composition analysis and XRD characterization.

Preparation of n-alkylated quaternary ammonium chitosan and its application in antibacterial finishing of rabbit hair fabric

Alkylated chitosan was obtained by alkylation of chitosan(CTS) with n-butyraldehyde, the product was then reacted with trichlorodihydroxypropyl triethyl ammonium chloride(CHPTAC-ethyl) to form n-alkylated quaternary ammonium chitosan. Its chemical structure was characterized by FTIR, and its physicochemical properties, such as viscosity-average molecular weight and solubility, were determined by viscosity and spectrophotometry. The antimicrobial activity of the modified chitosan was determined by the minimal antimicrobial method, and the minimum effective antimicrobial concentration (MIC) of the product against escherichia coli was 0.15g/L, which was better than the MIC value of the natural chitosan. Using citric acid as cross-linking agent and sodium hypophosphate as catalyst, the antibacterial finishing of rabbit hair fabric with modified chitosan showed that the antibacterial rate of n-alkylated quaternary ammonium chitosan to Escherichia coli was over 99.9%, and the antibacterial rate was better than that of natural chitosan, and it was a kind of good natural macromolecule antibacterial finishing agent for animal hair fabric.

Bio-synthesis of itaconic acid as an anti-crease finish for cellulosic fiber fabric.

Itaconic acid is an organic acid with a wide range of applications in the fields of polymer chemistry, pharmacy, agriculture, textile industry, etc. A bio-synthetic process of itaconic acid production in this study was carried out with Aspergillus terreus K17 having empty palm oil fruit bunches as a feedstock. Bio-synthesis of itaconic acid was compared with commercial maleic acid, itaconic acid and 1, 2, 3, 4-butanetetracarboxylic acid (BTCA) as anti-crease agents with sodium hypophosphate (SHP) as an esterification catalyst for cotton fabric finishing. The results showed that mechanical properties of cotton fabrics treated with bio-synthesized itaconic acid were better than those treated with the commercial ones whereas their whiteness index was lower. The best conditions for crease recovery were obtained from 8% w/v itaconic acid with 8% w/v SHP applied on cotton fabrics with a technique of 2-dip-2-nip, dried at 85 °C for 3 min and cured at 180 °C for 2 min. Even though the anti-crease properties of cotton fabrics treated with bio-synthesized itaconic acid were still lower than those treated with commercial maleic acid and BTCA, the finished cotton fibers retain the mechanical properties of cotton fabric. This study would be beneficial in producing itaconic acid as an eco-friendly anti-crease agent for cotton fabrics from waste empty palm oil fruit bunches by a bio-synthesis process.

Redox Dual-Cocatalyst-Modified CdS Double-Heterojunction Photocatalysts for Efficient Hydrogen Production.

Cadmium sulfide (CdS) as one of the most common visible-light-responsive photocatalysts has been widely investigated for hydrogen generation. However, its low solar–hydrogen conversion efficiency caused by fast carrier recombination and poor catalytic activity hinders its practical applications. To address this issue, we develop a novel and highly efficient nickel–cobalt phosphide and phosphate cocatalyst-modified CdS (NiCoP/CdS/NiCoPi) photocatalyst for hydrogen evolution. The dual-cocatalysts were simultaneously deposited on CdS during one phosphating step by using sodium hypophosphate as the phosphorus source. After the loading of the dual-cocatalysts, the photocurrent of CdS significantly increased, while its electrical impedance and photoluminescence emission dramatically decreased, which indicates the enhancement of charge carrier separation. It was proposed that the NiCoP cocatalyst accepts electrons and promotes hydrogen evolution, while the NiCoPi cocatalyst donates electrons and accelerates the oxidation of sacrificial agents (e.g., lactic acid). Consequently, the visible-light-driven hydrogen evolution of this composite photocatalyst greatly improved. The dual-cocatalyst-modified CdS with a loading content of 5 mol % showed a high hydrogen evolution rate of 80.8 mmol·g–1·h–1, which was 202 times higher than that of bare CdS (0.4 mmol·g–1·h–1). This is the highest enhancement factor for metal phosphide-modified CdS photocatalysts. It also exhibited remarkable stability in a continuous photocatalytic test with a total reaction time of 24 h.

Dimensional Stability of Wood Modified by Citric Acid

Wood samples of Pinus roxburghii and Populus deltoides were chemically modified by using three different treatments and cured by convection 0heating at 140° C for 8 h. The dimensional stability of the modified wood was determined by evaluating anti-swelling efficiency using the water soak/oven dry method. Citric acid modification resulted in better dimensional stability compared to control samples in both the species. The current study indicates that treatment with Citric acid 13.8% and Sodium hypophosphate 13.0% resulted in optimal improvement in dimensional stability of wood.

IMPROVE WEAR RESISTANCE BY NANO COMPOSITE ELECTRO LESS COATING FOR LOW ALLOY STEEL (NI-P-GRAPHENE)

Several experiments were carried out for the electroless coating process , Sodium hypophosphate with (10 , 14 and 24)g/l were added to achieve low , medium and high phosphorous in electro less coating for low alloy steel , the coating time (45 ,75 and 105)min and use different heat treatment temperatures (200,300 and 400)°∁ . Wear resistance was tested by ASTM G99 to evaluate the best result of creating a nano composite coating, in order to add Nano graphene , the graphene was added by (0.1 , 0.3 , 0.5 and 0.7) g /l. to coating bath . The FESEM filed emission scanning electron was conduct , x-ray diffraction to figure out the alloy compound on the layer coating , EDS energy dispersive spectroscopy to calculate the wt% P for low , medium and high , the pin on disk type were accomplished to evaluate the coating best result against the wear resistance. The results of the experiments showed that the coating with different weight% P, different coating time and different heat treatment temperature leads to improved wear resistance due to increased hardness and reduced friction coefficient by the addition of graphene.

Structural Identification and Electrical Conductivity Analysis of Sodium Hypophosphate Mixed Blend Polymer Electrolytes

Sodium hypophosphate is mostly applicable for improving protonic ion movement in the materials. Easy water absorbent blend polymers of poly vinyl-chloride and poly vinyl –pyrrolidone are mixed with sodium hypophosphate for using as polymeric membrane of electrochemical device applications. The various composition of solid electrolytes are prepared by solution casting techniques. Structural functional group of prepared materials of polymer matrices are characterized through FTIR spectroscopy. The electrical conductivity of the sample is determined through measured cole-cole plot of impedance data at different temperatures. The maximum electrical conductivity is calculated in the order of 10-6 Scm-1.

Direct Sodium Hypophosphite Fuel Cell System

The goal of the presented project is development a new type of direct sodium hypophosphite fuel cell (DSHFC) System, with Sodium Hypophosphite direct oxidation at the CoB2O4 based anode. Synthesized CoB2O4 was used as a catalyst of sodium hypophosphate oxidation [1,2]. CoB2O4 was annealed at 280˚C - 350˚C demonstrated best catalytic activity. In X-ray phase analysis of the sample show the X-ray diffraction pattern according to the ASTM standard of СoB2O4 (2.88,2.44, 2.03, 1.86 Å). Sodium Hypophosphite is oxidized in alkaline media. Hypophosphite-ion is adsorbed at metal oxide CoB2O4 surface, hydrogen atom, which is connected with catalyst surface by covalent bond, attenuates P-H bond and finally cleaves it; hydrogen is replaced by hydroxide-ion of water (1, 2) which causes hypophosphite transformation in phosphate. The overall anodic reaction will be (3) H2O=H++OH- (1) H2PO2 -ads + OH-ads = H2PO3 -ads+ H++ 2e- (2) NaH2PO2 + H2O = NaH2PO3 + 2H+ +2e- (3) The DSHFC anode was made by next steps: the CoB2O4 powder and carbon black XC72 powder 1:3 were mixed in isopropanol alcohol, as a binder was used polytetrafluoroethylene suspension and sonicated during 30 min. A carbon felt was used as an anode substrate and catalytic layer was covered bay spry-gun and heated at 250 oC during 5 min. the figure 1 show the DSHFC construction. The fuel Cell is undivided. As a cathode was used ordinary gas diffusion electrode for O2 reduction. The Anode and the cathode geometric surface area was 4 cm2 (2cm X 2cm) The Voltage –Ampere characteristics of the Direct Sodium Hypophosphite Fuel Cell was recorded with various concentrations of electrolyte X NaH2PO2 + Y NaOH, electrolyte was feed in to fuel cell by pump, oxygen to the cathode chamber was feed by air compressor (pressure 35-40 mm.H2O).Test were performed at room temperature. External load was changed from 10 000 Ω to 0.1 Ω. Current and voltage of DSHFC was recorded by multi-meters. In optimal conditions, electrolyte 1M NaH2PO2 + 2 NaOH, external load 1 Ω, the current density was 36 mA cm-1, the suitable power density was 13,5 mwt cm-1, open circuit potential was 1v References [1] Electroless plating: fundamentals and applications edited by G. O. Mallory, J. B. Hajdu [2] P.O. Nikoleishvili, at all, Russian Journal of Electrochemistry, 2015, Vol. 51, No. 7, pp. 665–671 Figure 1

Charge Stabilized Silver Nanoparticles Applied as Antibacterial Agents.

Monodisperse silver nanoparticle sols were synthesized via chemical reduction processes in aqueous environment without using polymeric stabilizing agents or surfactants. The sols obtained using various reducing agents; inorganic cell permeabilizers and organic phenolic compounds; inter alia gallic acid (GA) and tannin (TA) were thoroughly characterized by various physicochemical methods such as TEM, SEM, AFM, DLS and micro-electrophoresis. The antibacterial activity of the sols against two E. coli strains was characterized via the determination of the Minimum Bactericidal Concentration (MBC). All sols exhibited a pronounced bactericidal effect against the standard K12 strain, especially the GA and TA sols showing MBC concentration as low as 1-5 mg L(-1). In the case of the antibiotic resistant strain the highest activity (MBC of 10 mg L(-1)) was observed for the sol synthesized using sodium hypophosphate and sodium tripolyphosphate. Additionally, interactions of silver nanoparticles with bacteria cell were studied using TEM and AFM imaging. It was shown that the silver particles attach to the bacteria surface inducing disintegration, which enables their penetration inside the bacteria. Our measurements confirmed that the surface chemistry of silver nanoparticles can play a decisive role.

Citric Acid Cross-Linked Nanocellulose-Based Paper for Size-Exclusion Nanofiltration.

This article explores the effect of cross-linking of nanocellulose with citric acid for the development of novel paper filters for potential application within nanofiltration, including sterile (virus) filtration. Cladophora cellulose paper sheets were cross-linked by first soaking in 16 wt % citric acid in the presence of 1 wt % sodium hypophosphate overnight and then curing at 160 °C for 10 min in a hot-press. The cross-linked paper filter samples were then characterized with FTIR, AFM, N2 gas adsorption, and tensile strength analysis (dry and wet strength). The particle retention properties were further studied with respect to filtering of 20 nm Au nanoparticles with SEM and comparing the UV absorbance intensity of the starting solution and the filtrate. The wet strength of the paper filter was greatly improved following the cross-linking, although in the dry state, the paper becomes brittle. The improved wet strength of the paper filter enables increasing the pressure gradient applied for filtration without compromising the integrity of the filter. This is the first report in which a fully nature-derived paper filter is capable of removing tracer particles as small as 20 nm. It is concluded that citric acid cross-linking of nanocellulose is beneficial for developing paper based sterile (virus) removal industrial filters.

Increased formate-dependent H2 production from xylose in Enterobacter sp. CN1 transformed with a formate hydrogenlyase activator gene

Finding bacterial strains for effective hydrogen production and optimization of the fermentative conditions are two major approaches to promoting commercial application of bio-hydrogen. In the present study, we carried out experiments to examine factors that affected H2 yield in Enterobacter sp. CN1. The result showed that H2 could be produced from formate alone and the yields were positively correlated with formate concentrations. Moreover, the yield of H2 from xylose was significantly increased in the presence of formate, revealing that formate is not only a good carbon source but also promotes H2 production from xylose in strain CN1. The production of H2 from formate was not affected by pH; however, H2 production from xylose at pH 7 was higher than that at pH 6, no matter if formate is presence or absence in the medium. Further, H2 production from pyruvate was inhibited completely when sodium hypophosphate (HPP) was present, but formate-dependent H2 production was mostly not affected. In addition, H2 production from glucose or xylose was dramatically reduced but sill detectable in the presence of HPP, suggesting that formate hydrogenlyase is the main pathway responsible for H2 production from xylose in Enterobacter sp. CN1. To confirm the above hypothesis, the formate hydrogenlyase activator (fhlA) gene was cloned and over-expressed in strain CN1. Compared with the wild-type, recombinant CN1 strain increased H2 production per gram of xylose and per gram of cells by 10.5% and 18.8%, respectively, in the presence of xylose.

A novel self-assembled oligopeptide amphiphile for biomimetic mineralization of enamel.

BackgroundResearchers are looking for biomimetic mineralization of ena/mel to manage dental erosion. This study evaluated biomimetic mineralization of demineralized enamel induced by a synthetic and self-assembled oligopeptide amphiphile (OPA).ResultsThe results showed that the OPA self-assembled into nano-fibres in the presence of calcium ions and in neutral acidity. The OPA was alternately immersed in calcium chloride and sodium hypophosphate solutions to evaluate its property of mineralization. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed nucleation and growth of amorphous calcium phosphate along the self-assembled OPA nano-fibres when it was repetitively exposed to solutions with calcium and phosphate ions. Energy dispersive spectrometry (EDS) confirmed that these nano-particles contained calcium and phosphate. Furthermore, electron diffraction pattern suggested that the nano-particles precipitated on OPA nano-fibres were comparable to amorphous calcium phosphate. Acid-etched human enamel slices were incubated at 37°C in metastable calcium phosphate solution with the OPA for biomimetic mineralization. SEM and X-ray diffraction indicated that the OPA induced the formation of hydroxyapatite crystals in organized bundles on etched enamel. TEM micrographs revealed there were 20–30 nm nano-amorphous calcium phosphate precipitates in the biomimetic mineralizing solution. The particles were found separately bound to the oligopeptide fibres. Biomimetic mineralization with or without the oligopeptide increased demineralized enamel microhardness.ConclusionsA novel OPA was successfully fabricated, which fostered the biomimetic mineralization of demineralized enamel. It is one of the primary steps towards the design and construction of novel biomaterial for future clinical therapy of dental erosion.

Prevention of dentine caries using silver diamine fluoride application followed by Er:YAG laser irradiation: an in vitro study

To evaluate the preventive effect of Er:YAG laser (EYL) irradiation followed by silver diamine fluoride (SDF) application on dentine with cariogenic biofilm challenge. Twenty-four dentine slices were prepared from extracted sound human third molars. Each slice was cut into four parts for SDF application, followed by EYL irradiation (group SL), SDF application (group S), EYL irradiation (group L) and water (group W). The specimens were subjected to cariogenic biofilm challenge for 12 h, followed by immersion in a buffered remineralising solution containing calcium chloride and sodium hypophosphate for 12 h at 37 °C. Surface morphological changes in the specimens were examined using scanning electronic microscopy. Elemental analysis was performed using energy-dispersive X-ray spectrometry. Micro-mechanical properties were investigated by nano-indentation. The specimen surfaces of groups SL and L showed laser melting contours with narrowed dentinal orifices. Group S showed a partial tubular occlusion. A porous surface was observed in group W, indicating demineralisation. The mean (SD) fluoride weight percentages were 3.93 (0.91), 3.10 (0.61), 0.17 (0.09) and 0.32 (0.07) in groups SL, S, L and W, respectively, (p < 0.001; SL, S > L, W). The mean (SD) micro-hardness values in GPa were 1.84 (0.22), 0.49 (0.13), 0.41 (0.11) and 0.30 (0.06) in groups SL, S, L and W, respectively, (p < 0.001; SL > S > L, W). The mean (SD) elastic moduli in GPa were 75.1 (7.2), 20.0 (1.3), 24.3 (5.2) and 20.2 (2.8) in groups SL, S, L and W, respectively, (p < 0.001; SL > S, L, W). SDF application followed by EYL irradiation on a dentine surface increased its resistance to cariogenic biofilm challenge.