Phosphoric Acid Research Articles

Degradation of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) by ultraviolet activated hydrogen peroxide: Mechanisms, pathways and toxicity assessments

The ubiquity and ecotoxicity of tri (1,3-dichloro-2-propyl) phosphate (TDCPP) in aquatic environments make it essential to develop efficient related treatment techniques. The present research aims to systematically explore the mechanisms and toxicity changes of TDCPP degradation through UV-driven hydrogen peroxide process (UV/H2O2). The results revealed degradation efficiency of TDCPP attained 95 % with 0.5 mM H2O2, corresponding to a reaction rate constant (k) of 0.04919 min−1. Furthermore, three typical chlorinated OPEs (Cl-OPEs) were simultaneously degraded by the UV/H2O2 process, with different degradation efficiencies, according to the following order: TCEP<TDCPP<TCPP. The degradation efficiency was restricted under alkaline condition and the presence of humic acid (HA), nitrate (NO3–), chloride (Cl-), sulfate (SO42-), and dihydrogen phosphate (H2PO4-). A total of 12 intermediates were identified, which were generated through different pathways, including bond breaking, hydroxylation, and oxidation reactions. The Toxicity Estimation Software Tool (T.E.S.T) results demonstrated stronger mutagenicity and developmental toxicity of the TDCPP intermediates than parent compound. According to RNA sequencing results, UV/H2O2-based TDCPP degradation for 20 min and 60 min still had negative effects on Escherichia coli (E. coli). Indeed, the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results further suggested the stronger negative effect (e.g., damaging effects on the cell membrane, energy metabolism, and vitality) of the 20-min oxidation solution on E. coli, followed by those observed in without treatment and 60-min oxidation solution. Therefore, longer oxidation times are required in the UV/H2O2 process to decrease the toxicity of TDCPP.

Chemical composition and bio-efficacy of agro-waste plant extracts and their potential as bioinsecticides against Culex pipiens mosquitoes

Mosquitoes are considered one of the most lethal creatures on the planet and are responsible for millions of fatalities annually through the transmission of several diseases to humans. Green trash is commonly employed in agricultural fertilizer manufacturing and microbial bioprocesses for energy production. However, there is limited information available on the conversion of green waste into biocides. This study investigates the viability of utilizing green waste as a new biopesticide against Culex pipiens mosquito larvae. The current study found that plant extracts from Punica granatum (98.4 % mortality), Citrus sinensis (92 % mortality), Brassica oleracea (88 % mortality), Oryza sativa (81.6 % mortality), and Colocasia esculenta (53.6 % mortality) were very good at killing Cx. pipiens larvae 24 h post-treatment. The LC50 values were 314.43, 370.72, 465.59, 666.67, and 1798.03 ppm for P. granatum, C. sinensis, B. oleracea, O. sativa, and C. esculenta, respectively. All plant extracts, particularly P. granatum extract (14.93 and 41.87 U/g), showed a significant reduction in acid and alkaline phosphate activity. Additionally, pomegranate extract showed a significant decrease (90 %) in field larval density, with a stability of up to five days post-treatment. GC–MS results showed more chemical classes, such as terpenes, esters, fatty acids, alkanes, and phenolic compounds. HPLC analysis revealed that the analyzed extracts had a high concentration of phenolic and flavonoid components. Moreover, there are many variations among these plants in the amount of each compound. The docking interaction showed a simulation of the atomic-level interaction between a protein and a small molecule through the binding site of target proteins, explaining the most critical elements influencing the enzyme's activity or inhibitions. The study's findings showed that the various phytochemicals found in agro-waste plants had high larvicidal activity and provide a safe and efficient substitute to conventional pesticides for pest management, as well as a potential future in biotechnology.

Highly-efficient method for chitin nanocrystal production using solid-state phosphoric acid hydrolysis

Highly-efficient method for chitin nanocrystal production using solid-state phosphoric acid hydrolysis

Dancing bubble sonoluminescence in phosphoric acid solution

Abstract Sonoluminescence is more distinctly observed in phosphoric and sulfuric acid, which exhibit high viscosity and lower vapor pressures relative to water. Within an 85-wt% phosphoric acid solution saturated with argon (Ar), variations in the light-emitting regimes of bubbles were noted to correspond with increments in the driving acoustic intensity. Specifically, the bubbles were observed to perform a dance-like motion 2 cm below the multi-bubble sonoluminescence (MBSL) cluster, traversing a 25-mm2 grid during the camera exposure period. Spectral analysis conducted at the beginning of the experiment showed a gradual attenuation of CN (B2Σ–X2Σ) emission concurrent with a strengthening of Ar (4p–4s) atom emission lines. The application of a theoretical temperature model to the spectral data revealed that the internal temperature of the bubbles escalates swiftly upon their implosion. This study is instrumental in advancing the comprehension of the underlying mechanisms of sonoluminescence and in the formulation of a dynamic model for the behavior of the bubbles.

X-ray Induced Cycling of Rare-Earth Elements between Bulk and Interfacial Liquid.

Reversible cycling of rare-earth elements between an aqueous electrolyte solution and its free surface is achieved by X-ray exposure. This exposure alters the competitive equilibrium between lanthanide ions bound to a chelating ligand, diethylenetriamine pentaacetic acid (DTPA), in the bulk solution and to insoluble monolayers of extractant di-hexadecyl phosphoric acid (DHDP) at its surface. Evidence for the exposure-induced temporal variations in the lanthanide surface density is provided by X-ray fluorescence near total reflection measurements. Comparison of results when X-rays are confined to the aqueous surface region to results when X-rays transmit into the bulk solution suggests the importance of aqueous radiolysis in the adsorption cycle. Amine binding sites in DTPA are identified as a likely target of radiolysis products. The molecules DTPA and DHDP are like those used in the separation of lanthanides from ores and in the reprocessing of nuclear fuel. These results suggest that an external source of X-rays can be used to drive rare-earth element separations. More generally, use of X-rays to controllably dose a liquid interface with lanthanides could trigger a range of interfacial processes, including enhanced metal ion extraction, catalysis, and materials synthesis.

Quantitative Interpretation of Potentiodynamic Polarization Curves Obtained at High Scan Rates in Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is becoming the tool of choice for the investigation of localized metal corrosion. Typically, potentiodynamic polarization measurements in scanning electrochemical cell microscopy are performed at high potential scan rates. However, Tafel extrapolation applied to high-scan-rate potentiodynamic polarization curves would yield inaccurate corrosion kinetics due to the interference of double-layer charging current or mass transport of species in the metal oxide. Instead, the high field model was used to simulate the potentiodynamic polarization curves of pure aluminum at 25, 50, 100, and 200 mV/s in neutral and acidic phosphate solutions, thus enabling quantitative analysis of local corrosion kinetics by fitting the potentiodynamic polarization curve.

Morphological study of remineralization of the eroded enamel lesions by tyrosine-rich amelogenin peptide

BackgroundTyrosine-rich amelogenin peptide (TRAP) is the main amelogenin digestion product in the developmental enamel matrix. It has been shown to promote remineralization of demineralized enamel in our previous study. However, direct evidence of the effect of TRAP on the morphology and nanostructure of crystal growth on an enamel surface has not been reported. This study aimed to examine the effect of TRAP on the morphology of calcium phosphate crystals grown on early enamel erosion using a pH-cycling model.MethodsEroded lesions were produced in human premolars by 30-second immersion in 37% phosphoric acid. Forty-five samples of eroded human premolar enamel blocks were selected and randomly divided into 3 groups: deionized water (DDW, negative control); 100 µg/mL TRAP, and 2 ppm sodium fluoride (NaF, positive control group). For 14 days, the specimens were exposed to a pH-cycling model. Using scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods, the surface morphology, calcium-phosphorus ratio, and enamel surface roughness were examined. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to assess crystal characteristics.ResultsAfter pH-cycling, compared to the two control groups, the surface of the eroded enamel of the peptide TRAP group shows a large number of new, densely arranged rod-like crystals, parallel to each other, regularly arranged, forming an ordered structure, with crystal morphology similar to that of natural enamel. The crystals are mostly hydroxyapatite (HA).ConclusionThis study demonstrates that the peptide TRAP modulates the formation of hydroxyapatite in eroded enamel and that the newly formed crystals resemble natural enamel crystals and promote the remineralization of enamel, providing a promising biomaterial for remineralization treatment of enamel lesions.

Synthesis and Characterization of Nano-Crystallite Triple Super Phosphate (TSP) from Marine Mollusk Waste: Babylonia japonica, Oliva sayana, and Conasprella bermudensis.

The study aims to synthesize nano-crystallite TSP using renewable, low-cost, waste marine mollusk from three different species such as Babylonia japonica, Oliva sayana, and Conasprella bermudensis. The molar ratio of phosphate to calcium in triple superphosphate [TSP, Ca(H2PO4)2.H2O] significantly impacts its properties and fertilizer performance, in this case, we kept the ratio to 2. Raw TSP has a high phosphate content and lower calcium content. The synthesized TSP was analyzed using various techniques including TGA, XRD, EDX, FT-IR, and SEM. The study utilized multiple XRD model equations to analyze crystallite size ( ), with all models except the Liner straight-line method providing higher estimates for synthesized TSP. Furthermore, the values for stress (2×107 to 4×107 N/m2), strain (4×10-4 to 9×10-4), as well as energy density (4.54×103 to 16.27×103 J/m3) were also calculated for the synthesized product. However, the preferential growth calculation indicates that (010), (021), and (020) planes are the most thermodynamically stable planes for the growth of the synthesized TSP. Apart from that, FTIR result confirms that CaO, -OH, as well as PO4 3- functional groups are present in the synthesized products. This research suggests that marine mollusks can be utilized as a calcium precursor for P-fertilizer and 60 % phosphoric acid, thereby reducing production costs by eliminating additional dehydrating. Additionally, waste marine mollusk shells could be utilized as an alternative to the production of phosphate-based fertilizer.

Synthesis and characterisation of superior AC/ZnO NPs biocomposite for hexavalent chromium Cr(VI) adsorption

This study aims to synthesize biocomposite by combining banana stem activated carbon (AC) and ZnO Nanoparticles (NPs) to evaluate their adsorption potential towards hexavalent chromium (Cr (VI)) (20 mg/L). The AC used was successfully synthesized by an impregnation method using phosphoric acid (H3PO4) for 24 h, followed by a carbonization method. ZnO NPs were synthesized using the direct precipitation method using zinc acetate dihydrate (0.2 M) and KOH (0.4 M) as precursors. The AC/ZnO NPs biocomposite was fabricated using the mechanical alloying method at a frequency of 10 Hz for 30 min. The FTIR results show that both adsorbents, namely pure AC and AC/ZnO NPs have abundant functional groups. XRD results show the adsorbent is amorphous with pure AC at 89.95% and AC/ZnO NPs biocomosite at 56.49%. SEM results showed that the morphology of AC resembled crushed bovine bone marrow, and the morphology of ZnO NPs showed a marshmallow-like shape. The UV–vis spectrometer test results show that at the absorption peak of 350 nm the Cr (VI) removal efficiency slowly decreases and disappears at a dose variation of 1.5 g pure AC, 2 g biocomposite AC/ZnO NPs, and 2 g pure AC with Cr (VI) removal efficiency of 99.61%, 99.64%, and 99.83% respectively. Finally, we can report that the high degradation ability for Cr (VI) can be related to thesharp peak of –C=O group, reduced ΔLO−TO, and smaller average crystallite size in AC/ZnO NPs biocomposite.

Coconut Shell Carbon Preparation for Rhodamine B Adsorption and Mechanism Study.

Phosphoric acid is used as a chemical activator to prepare coconut shell carbon (PCSC), and for investigating rhodamine B (RhB) adsorption performance. The optimal conditions for the preparation of PCSC (calcined temperature, phosphoric acid concentration), and the influence of adsorption conditions (concentration, pH, etc.) on RhB and the recovery performance of optimal carbon are investigated. Experimental results show that when the amount of PCSC (600 °C, 2 h) is 0.2 g, the initial RhB concentration is 10 mg/L, pH = 6, and the adsorption time is 30 min, it can have 95.84% RhB adsorption efficiency. Liquid ultraviolet spectroscopy also supports this adsorption performance. Characterization data showed that hydroxyl and ester groups, aromatic structures, and PO43- existed on the surface of PCSC, and the amount decreased with increasing calcined temperature. PCSC has a BET (N2) surface area of 408.59 m2/g and has a micropore distribution, EDS-detected P content is 3.91%. SEM showed that the PCSC formed micropores which could better adsorb RhB. The kinetic and thermodynamic analysis of the adsorption of RhB by PCSC showed that the adsorption process was in accord with quasi-secondary kinetic equations and ΔGθ was between -1.65 and -18.75 kJ/mol. The adsorption was a physical adsorption and a spontaneous endothermic reaction, and the obtained PCSC sorption isotherms were classified as Langmuir-type. The RhB adsorption mechanism on PCSC includes pore diffusion, hydrogen bonding, and π-π conjugation. The PCSC prepared by H3PO4 modification has superior adsorption and recycling performance for RhB, providing a reference for the preparation of other biomass carbon materials for the treatment of dye wastewater.

Comparative Study of Adsorbents for Treatment of Industrial Effluent

Water contaminated with various impurities is considered as wastewater and industrial wastewater obtainedfrom industries is known as effluent. The industrial effluent adversely affects the aquatic ecosystems,deteriorate human health, and degrades overall environmental quality. Treatment of such effluent withadsorbent is one of the most efficient and cost-effective method. In the present study, industrial effluent wastreated with various bio-adsorbents obtained from orange peels, cotton, neem tree bark. Effect of adsorptionon parameters like pH, COD, BOD, TDS and TSS were determined and their results were compared withcommercial grade activated charcoal. For majority of the parameters, the effectiveness of adsorbent varied as:activated charcoal &gt; tree bark-based adsorbent &gt; cotton-based adsorbent &gt; orange peels-based adsorbent.Effect of pretreatment- acid treatment- was also examined for cotton and tree bark-based adsorbent.Phosphoric acid was proven to be better acid for pretreatment in comparison with sulfuric acid. For tree barkbased adsorbent treated with phosphoric acid, % removal for COD, BOD, TDS and TSS were 46.5 %, 57.06%, 35.51% and 90.43% respectively

Effectiveness of liquid rubber dam in improving dental isolation: An in vitro study

A liquid rubber dam is used as a gingiva protector and to ameliorate the sealing quality around the tooth. No information about the mechanical properties of liquid rubber dam and its efficiency in tooth isolation was reported in the literature. Therefore, the purpose of the present in vitro study was to evaluate the morphological changes after contact with different solutions, microleakages, bond strength to enamel, and mechanical properties of two different liquid rubber dams (Top dam “TD” and OpalDam™ “OD”). Scanning electron microscopy (SEM) was used to investigate the morphological changes. Compression strength and viscosity tests were used to investigate the mechanical properties. A shear bond strength test was performed to evaluate the bond strength of liquid rubber dams to enamel. Solubility was performed to investigate the effect of water after 90 min of contact. Finally, the microleakage tests were performed by using methylene blue. Data were statistically analyzed. No presence of methylene blue was detected after 30, 60, and 90 min of immersion for both dams, giving both products a good sealing ability in time. SEM demonstrated morphological changes of the materials’ surfaces after contact with bleaching and phosphoric acid products. TD demonstrated higher bond strength to enamel as well as higher compression strength at 90 min compared to OD. However, TD demonstrated higher solubility than OD, which facilitates its deposition in layers. The shear viscosity of the TD was higher than that of the OD material by about a factor of 60. Within the limitations of the present study, liquid rubber dam can ensure the sealing ability. TD seems to be more resistant and has higher bond strength to tooth structure compared to OD.

Ionomeric Binders for High Temperature Proton Exchange Membrane Fuel Cells.

High-temperature proton exchange membrane fuel cell (HT-PEMFC) based on phosphoric acid doped polybenzimidazole membrane (PBI/PA) operating at 120-200 °C can provide insensitivity to carbon monoxide (CO) and simplified managements of water and heat and thus attract significant global attention. However, one significant drawback is its low utilization of precious metal catalysts resulted from the PA poisoning and inefficient three-phase boundary. Studies of binder materials in catalyst layers for HT-PEMFC are gradually emerging and there are few literature reviews on this important topic. The purpose of this review is to describe the various types of binders based on their molecular structure and electrochemical properties, with particular emphasis on catalyst layer for fuel cells. Importantly, this review provides a better understanding of relationship between fuel cell performance and the gas permeability and conductivity of different binders. Then, future directions of research and development in binder materials of HT-PEMFC are pointed out.

Production of hydrochar from the hydrothermal carbonisation of food waste feedstock for use as an adsorbent in removal of heavy metals from water

AbstractIn this research, discarded butternut peels were converted into hydrochar products through hydrothermal carbonisation (HTC), with adjustments made to the temperature (ranging from 180 to 260℃) and residence time (spanning 45–180 min). The findings indicated that both the temperature and time of carbonisation significantly influenced the yield of hydrochar (HC), as well as its physiochemical and structural properties. Higher temperatures and prolonged residence time led to decreased yield, elevated fixed carbon content and an increased fuel ratio. Furthermore, raising the process conditions increased HHV and reduced the oxygen-containing functional groups. The HC yield dropped from 28.75 to 17.58% with increased carbonisation temperature and time. The findings of this study also suggest that modified hydrochar is a promising material for removing heavy metals from wastewater. It is a relatively low-cost and abundant material that can be produced from various biomass feedstocks, including food waste. In addition, it is a sustainable and environmentally friendly option for wastewater treatment. Hydrochar-based systems offer several advantages over traditional methods of heavy metal removal, such as chemical precipitation and ion exchange. The unique physicochemical characteristics of hydrochar, including its porous structure and oxygen-rich functional groups, offer a high surface area and more binding sites for heavy metal ions. By changing the physicochemical properties of hydrochar with chemicals like phosphoric acid, it is possible to increase its adsorption capacity. The Freundlich isotherm was the best fit for the adsorption data for all three metal ions (Pb2+, Cu2+ and Cd2+), indicating that the adsorption process is multilayer and heterogeneous.

Preparation of high temperature proton exchange membranes with multilayered structures through alternate deposition of carbon dots@Metal organic framework and Sulfonated Poly(Ether Ketone)

High temperature proton exchange membranes (HTPEMs) with multilayered structures based on carbon dots@metal organic framework (CDs@MOF) and Sulfonated Poly(Ether Ketone) (SPEEK) have been prepared with the spin coating technique. In this research, carbon dots (CDs) are self-assembled with metal organic framework (MOF) to form the composite of CDs@MOF. Successive proton conduction channels consisting of CDs@MOF and sulfonated groups in SPEEK facilitate to conduct protons in multilayered structures of the prepared composite membranes. Additionally, CDs@MOF can combine phosphoric acid (PA) molecules deriving from the formed intermolecular hydrogen bonding. The proton conductivity is further improved because of the multilayered structures reducing the proton conduction resistance. Specifically, the (SPEEK/40%CDs@MOF)3/PA membrane exhibits the maximum proton conductivity of (5.02 ± 0.64) × 10−2 S/cm at 160 °C. Notably, the proton conductivity can retain 1.53 × 10−2 S/cm at 80 °C after a 200 h non-stop test. The open circuit voltage peak and power density of a single fuel cell based on the (SPEEK/40%CDs@MOF)3/PA membrane respectively reach 0.95 V, 258.2 mW/cm2 at 100 °C and 0.96 V, 369.9 mW/cm2 at 120 °C.

Effect of PFDTS/TiO2 Coating on Microstructure and Wetting Behavior of Phosphogypsum.

Phosphogypsum (PG) constitutes a form of solid byproduct emanating from the manufacturing process of wet-process phosphoric acid. The fabrication of one metric ton of wet-process phosphoric acid entails the generation of approximately five tons of phosphogypsum, a highly prolific and economically viable waste stream. If we can effectively solve the problem of poor hydrophobicity of phosphogypsum, it is possible to replace cement and other traditional cementitious materials. In this way, we can not only improve the utilization rate of phosphogypsum but also obtain significant economic and environmental benefits. In the present investigation, hydrophobic surface coatings were synthesized and applied onto the surface of α-hemihydrate phosphogypsum (α-HPG) utilizing sol-gel processing and impregnation techniques. After hydroxylating α-HPG with alkaline solution (OH-α-HPG), titanium dioxide nanoparticles (TiO2) hybridized with perfluorodecyltriethoxysilane (PFDTS) were grafted on its surface. The assessment of the hydrophobic properties of the coatings was conducted through water contact angle measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) analyses. The contact angle remained above 124.2° after strong acidic and alkaline immersion and 50 tape adhesion experiments with good chemical stability and durability, and the mechanism of surface hydrophobicity modification was discussed. The experimental outcomes demonstrated a notable increase in the hydroxyl group concentration on the α-HPG surface following hydroxylation, significantly enhancing the attachment rate of PFDTS and TiO2 onto the HPG surface. PFDTS and TiO2 can undergo chemical interaction with hydroxyl groups, facilitating their robust adsorption onto the surface of OH-α-HPG through chemisorption mechanisms. After bonding the OH-α-HPG surface with PFDTS and TiO2 via hydrogen bonding, the otherwise hydrophilic α-HPG surface acquired excellent hydrophobicity (OH-α-HPG-PT, contact angle (CA) = 146.7°). The surface modification of α-HPG through hydroxylation and hydrophobicity enhancement significantly augmented the compatibility and interfacial interplay between α-HPG and PT. This research successfully enhanced the hydrophobic properties of α-HPG, profoundly showcasing its immense potential within the construction industry and the realm of comprehensive solid waste utilization.

Synthesis of Lactams via a Chiral Phosphoric Acid-Catalyzed Aniline Cyclization.

The enantioenriched lactams disclosed in this work are synthesized concisely in four steps. In the penultimate reaction, a benzylamine species complexes with a chiral phosphoric acid to produce benzo-fused δ-lactams equipped with an all-carbon quaternary stereocenter. Partial and full reductions were carried out on the ester and amide moieties, and a Suzuki-Miyaura cross-coupling expanded the molecule from the aromatic ring. Finally, our method was successful at a >1 g scale, indicating that the method has important practical use.

“Treating Waste with Waste”: Utilizing Phosphogypsum to Synthesize Porous Calcium Silicate Hydrate for Recovering of Fe2+ from Pickling Wastewater

Phosphogypsum is a by-product of the wet-process phosphoric acid production, and it is rich in Ca and S. Long-term storage of Phosphogypsum can cause serious pollution to the environment; therefore, promoting the sustainable utilization of Phosphogypsum is crucial. This study proposes the use of Phosphogypsum and silicic acid in a sodium hydroxide solution for the hydrothermal synthesis of porous calcium silicate hydrate adsorbent, which is used for adsorbing Fe2+ from simulated hydrochloric acid pickling wastewater. Under the optimal synthesis conditions (37.5 g/L of NaOH, calcium/silicon ratio of 1.0, liquid/solid ratio of 15:1 mL/g, 110 °C, and 4 h), the conversion rate of SO42− in Phosphogypsum is 87.41%. Porous calcium silicate hydrate exhibits excellent OH− release capability in Fe2+-containing pickling wastewater. The adsorption process for Fe2+; is mainly chemical adsorption, involving ion exchange between Ca2+ and Fe2+, as well as complexation reactions of O-Si-O group, -OH group, and Si-O group with Fe2+. This technology aims to provide a solution for the sustainable utilization of Phosphogypsum and the recovery of Fe2+ from pickling wastewater, which has significant practical importance.

Coconut shell carbon via phosphoric acid activation for rhodamine B, malachite green, and methylene blue adsorption – equilibrium and kinetics

This study was aimed at evaluating the removal of different cationic dyes onto phosphoric acid-activated coconut shell carbon. The activated carbon was characterized for surface functional groups, thermal decomposition profiles, surface morphology, and textural properties. The specific area was recorded as 1,221 m2/g with 100% mesoporosity. On molecular basis, the activated carbon adsorbs malachite green, methylene blue, and rhodamine B at maximum capacities of 1.52 mmol/g, 0.80 mmol/g, and 0.58 mmol/g, respectively. It indirectly implies the selectivity of activated carbon toward malachite green, and behaves differently due to steric hindrance of dye molecules. All equilibrium data obeyed Langmuir model, while the kinetic data are closely fitted to pseudo-second order model as concentration increases. To conclude, coconut shell activated carbon is more effective to remove malachite green compared to methylene blue and rhodamine B.

Asymmetric 1,4-Reduction of Pyrano[2,3-b]indoles with Hantzsch Ester by Chiral Phosphoric Acid.

A highly regioselective and enantioselective transfer hydrogenation of pyrano[2,3-b]indoles with Hantzsch ester has been successfully realized using spiro-chiral phosphoric acid, affording a series of optically active 1,4-reductive adducts, 4,9-dihydropyrano[2,3-b]indoles, in 34-99% yields with 61-99% ee.