Molecular insights into the catalytic oxidation of methanol-to-olefins wastewater with phosphoric acid modified sludge biochar

With the development of methanol-to-olefin (MTO) process, the effective disposal of wastewater was one key factor for the long-period and benign development of this technology. Herein, a sludge-based biochar catalyst (GSC-P) was synthesized and used in photo-Fenton reaction for the degradation of MTO wastewater from the outlet of a biological aerated filter. More iron was distributed on the surface of GSC-P catalyst, facilitating the photo-Fenton oxidation of MTO wastewater, with chemical oxygen demand (COD) removal rate of 75.4% and total organic carbon (TOC) removal rate of 62.5%. The 2223 unique molecular formulas assigned by a Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in the original MTO wastewater showed that CHO compounds shared the lowest peak numbers (20.2%) but the highest peak abundance (51.6%) among the four groups. Besides, lipids, unsaturated hydrocarbons, lignins and proteins were the main structural types. After photo-Fenton treatment of 60 min, there were 56.7%-74.0% of compounds removed by the analysis of van Krevelen diagram, indicating that the MTO wastewater was degraded efficiently. Three possible evolution processes of dissolved organic matters during the photo-Fenton reaction were disclosed at the molecular-level.

Preparation of formate-free PMA@MOF-808 catalysts for deep oxidative desulfurization of model fuels

Due to the increasingly serious environmental problems caused by the combustion of sulfides in fuel, deep desulfurization of fuel became particularly urgent. Herein, the catalyst (PMA@MOF-808) of the Zr-based metal-organic framework (MOF-808) encapsulating phosphomolybdic acid (PMA) was prepared via a one-pot hydrothermal method. Besides, the formate ions of PMA@MOF-808 were removed by posttreatment with methanol, resulting in formate-free PMA@MOF-808-H catalysts with unsaturated open metal sites. The as-synthesized catalysts were systematically characterized by XRD, FT-IR, SEM, BET, TGA, ¹H NMR and XPS. The catalysts were also applied in catalytic oxidation desulfurization of fuel. The results indicated that the introduction of PMA and the removal of formate ions can improve the desulfurization performance of catalysts. Formate-free 0.2-PMA@MOF-808-H catalyst can reach 100% desulfurization rate for DBT. Besides, the kinetic properties were studied, and the apparent activation energy was 29.34 kJ/mol.

Thermal properties and pyrolysis kinetics of phosphate-rock acid-insoluble residues

In the phosphorous-sulphur two-step process for the clean production of phosphoric acid, a phosphate-rock acid-insoluble residue (PAIR) is a solid filter residue obtained via the phosphoric acid acidolysis of phosphate rock (PR). PAIR combined with other raw materials can be used to prepare cement, ceramics and glasses, opening a potential avenue for large-scale PAIR utilisation. However, the preparation of such materials requires high-temperatures calcination. Understanding the high-temperature thermal properties of PAIR can enable its more targeted comprehensive utilisation or disposal. In this study, the thermal properties and pyrolysis kinetics of PAIR were systematically studied using a multiple heating rate method based on thermogravimetric analysis and a kinetic model. Results showed that from room temperature to 1200 °C, the main changes in the PAIR were the complete removal of fluorine and sulphur, partial removal of phosphorus and conversion of quartz to cristobalite. Moreover, during these processes, H₂O(g), NH₃, N₂, CO₂, SO₂, P₂O₅(g), CO, CF₃⁺ and organic gases were volatilised. Herein, the pyrolysis kinetics of PAIR is divided into five stages. Stage 1 (conversion rate ɑ: 0.05-0.2) conforms to the random nucleation and growth as well as the Avrami-Erofeev (n = 2/3) mechanism; the corresponding mechanism function is F(ɑ) = [-Ln(1 - ɑ)]^2/3. Stage 2 (ɑ: 0.2-0.4) conforms to the first-order chemical reaction mechanism; the corresponding mechanism function is F(ɑ) = -Ln(1 - ɑ). Stage 3 (ɑ: 0.4-0.6) conforms to the phase boundary-controlled reaction and one-dimensional movement mechanism; the corresponding mechanism function is F(ɑ) = ɑ. Stage 4 (ɑ: 0.6-0.8) conforms to the three-dimensional diffusion process (Jander model); the corresponding mechanism function is F(ɑ) = [1 - (1 - ɑ)^1/3]². Stage 5 (ɑ: 0.6-0.95) conforms to the one-dimensional diffusion process; the corresponding mechanism function is F(ɑ) = ɑ².

Phosphomolybdic acid-catalyzed oxidation of waste starch: a new strategy for handling the OCC pulping wastewater

When old corrugated cardboard (OCC) is returned to the paper mill for repulping and reuse, the starch, which is added to the paper surface as a reinforcement agent, is dissolved into the pulping wastewater. Most of the OCC pulping wastewater is recycled to save precious water resources; however, during the water recycling process, the accumulation of dissolved starch stimulates microbial reproduction, which causes poor water quality and putrid odor. This problem seriously affects the stability of the papermaking process and product quality. In this study, phosphomolybdic acid (H₃PMo₁₂O₄₀, abbreviated as PMo₁₂) was utilized to catalyze the waste starch present in papermaking wastewater to monosaccharides, realizing the resource utilization of waste starch. The results showed that the optimized yield of total reducing sugar (78.68 wt%) and glycolic acid (12.83 wt%) was achieved at 145 °C with 30 wt% PMo₁₂ at pH 2, which is equivalent to 91.51 wt% starch recovered from wastewater for resource utilization. In addition, the regeneration of the reduced PMo₁₂ was realized by applying a potential of 1 V for 2 h. Overall, this study has theoretical significance and potential application value for resource utilization of waste starch in OCC pulping process and cleaner management of OCC waste paper.

Exploring the potential effect of Achnatherum splendens L.-derived biochar treated with phosphoric acid on bioavailability of cadmium and wheat growth in contaminated soil

Biochar remediation efficiency could be enhanced through numerous treatments such as acids treatment. Still, there has little work done on H₃PO₄-treated biochar particularly biochar derived from Achnatherum splendens L. feedstock. Therefore, the present study has been conducted to further explore the potential effect of A. splendens L.-derived biochar treated with H₃PO₄ on bioavailability of Cd and wheat growth in Cd contaminated soil. Phosphoric acid and untreated biochar each applied at the rate of 1% and 2% to Cd contaminated/spiked soil in pots and having one contaminated/spiked control without biochars amendment. The results show that 2% phosphoric acid-treated biochar has the most significant increase in plant height, shoot dry weight, and grain yield of wheat as compared to contaminated control. As compared to contaminated control, maximum improvement in total chlorophyll contents, photosynthetic rate, transpiration rate, and stomatal conductance occurred with 2% phosphoric acid-treated biochar. The 2% phosphoric acid-treated biochar also declined bioavailable Cd in soil by 53%, and its accumulation in shoot and grain by 65% and 90%, respectively, compared to contaminated control. Overall, phosphoric acid-treated biochar most effectively immobilized Cd in soil and reducing its uptake and translocation to grains. Therefore, A. splendens L.-derived biochar treated with phosphoric acid could be successfully utilized for remediation of contaminated soil.

Preparation of phosphoric acid modified antibiotic mycelial residues biochar: Loading of nano zero-valent iron and promotion on biogas production

Antibiotic mycelial residues (AMRs), as recyclable hazardous waste, can realize efficient utilization by reasonable treatment. To solve the problems of undeveloped pore structure and low specific surface area existed in AMR biochar, this study first modified biochar by phosphoric acid (H₃PO₄) to prepare PBC (H₃PO₄-modified biochar). Then, PBC was used as carrier to load nano zero-valent iron (nZVI) for preparation of nZVI/PBC. Finally, the biochar materials were used to promote anaerobic digestion (AD) of corn straw. The results showed that H₃PO₄-modification can effectively improve the specific surface area, pore structure, and electron donating capacity of AMRs biochar. The using of PBC as carrier to load nZVI attenuated the agglomeration of nZVI particles. Both PBC and nZVI/PBC improved the AD process, with biogas yield enhanced by 29.63% and 29.26%, respectively. The nZVI/PBC exhibited higher ability in maintaining the stability of AD system and promotion of fiber degradation than PBC.

Surface modification of spent coffee grounds using phosphoric acid for enhancement of methylene blue adsorption from aqueous solution

In this study, the surface of the spent coffee grounds (SCG) was activated using phosphoric acid to increase the removal efficiency of methylene blue (MB) in aqueous solution, which is one of the harmful substances emitted in industrial processes. According to Fourier transform infra-red analysis, after phosphorylation of the SCG (PSCG), P = O group, P-O-C (aromatic) bond, P = OOH and P-O-P were newly introduced on the surface of the adsorbent, and the peaks of carboxyl groups and OH-group were large and broad. In addition, the surface area and mesopore range of the PSCG adsorbent were increased, and the structure changed, which enabled easy adsorption of MB. The process of adsorbing MB from aqueous solution using PSCG was more suitable for the pseudo-second order and Langmuir models, and the adsorption process was closer to chemisorption than physical adsorption. The maximum adsorption capacity of PSCG was 188.68 mg/g. As a result of the reuse test, PSCG showed excellent performance with a high removal efficiency of 90% up to four consecutive uses. PSCG modified with phosphoric acid, an abundant lignocellulose-based biosorbent that is readily available everywhere, is a promising adsorbent capable of adsorbing MB in aqueous solution.

Dihydroxybenzene isomers electrochemical sensor based on activated carbon sensitive material activated by mechanochemistry and low-dosage phosphoric acid

A dihydroxybenzene isomers electrochemical sensor based on bamboo activated carbon (MCPBAC) sensitive material activated by mechanochemistry and low-dosage phosphoric acid was fabricated in this work. The sensor, modified by MCPBAC with GCE, can significantly distinguish and sensitively measure hydroquinone (HQ) and catechol (CC). The MCPBAC exhibits a well-developed porous structure, high specific surface area, and good electrical conductivity. Using differential pulse voltammetry (DPV), wide linear ranges for both HQ and CC are 0.6-600 μM, with low detection limits (S/N = 3) for both of 0.2 μM. The dihydroxybenzene isomers electrochemical sensor has wide application prospects in the determination of trace HQ and CC in environmental water.

Heterogeneous photooxidation of 6:2 polyfluoroalkyl phosphoric acid diester on dust mineral components under simulated sunlight and the influence of relative humidity and oxygen

Polyfluoroalkyl phosphoric acid diesters (diPAPs) have been widely and increasingly detected in various environmental mediums. The degradation of diPAPs brings perfluoroalkyl carboxylic acids (PFCAs) concerned of adverse health effects. DiPAPs mainly occur in particulate matter in ambient air and their photo-degradation behaviors have not been investigated. In this study, heterogeneous photo-degradation of 6:2 diPAP was studied on four model mineral components in ambient dust. 6:2 diPAP was found to undergo a fast degradation on titanium dioxide (TiO₂) particles as well as on artificial mineral dust containing TiO₂ (2.67% in mass) to produce C5-C7 PFCAs and other intermediates. Based on monitored intermediates and further degradation tests on important intermediates, thermodynamic calculation of energy barrier and Gibbs Free Energy was used to explain the observed degradation patterns and accordingly the degradation pathways of diPAPs were proposed. The increase in relative humidity promotes the production of hydroxyl radicals, which enhances the hydrolysis of 6:2 mono- and di-PAPs and the yield of C5 and C7 PFCAs. Oxygen is critical for radical formation, which bypasses the production of fluorotelomer carboxylic acid. Results of this study for the first time demonstrate that diPAP may account for additional PFCA sources in both indoor and outdoor environments and the heterogeneous degradation pathways were different from those of volatile fluorotelomer alcohols.

The quality of etched enamel in different regions and tooth types and its significance in bonding and the development of white spot lesions

OBJECTIVES

To quantify differences in the etch quality of enamel within and between human teeth, which has not previously been attempted.

MATERIALS AND METHODS

The buccal right and left halves of 27 extracted human teeth were randomly allocated to scanning electron microscopy (SEM) or micro-computed tomography (μCT) for evaluation. The buccal surfaces were pumiced, etched with 37% phosphoric acid gel etchant for 15 seconds, rinsed, and air dried. Each tooth was divided into three regions (incisal, middle, and cervical) and viewed after etching at 1200× magnification with SEM. The μCT scans were taken before and after etching to calculate apparent and material mineral densities.

RESULTS

SEM showed greater aprismatic enamel and poorer etch quality (ie, significantly less percentage enamel) for the posterior than anterior teeth and for the cervical region than for the incisal and middle regions of all teeth. Although there were no density differences prior to etching, μCT demonstrated that etching increased material density significantly more for the anterior than posterior teeth. Prior to etching, the enamel in the cervical regions was significantly less dense than the enamel in the middle or incisal regions. Etching significantly increased the material density of all three regions, which decreased initial regional differences. After etching, the apparent density of the cervical region remained significantly lower than the densities of the other two regions.

CONCLUSIONS

Based on SEM and μCT, there is greater aprismatic enamel and inferior etch quality in the cervical regions of all tooth types and is clinically significant in explaining the failure of sealant retention and the propensity for white spot lesions.

The Effect of Deproteinizing Agents on Bond Strength of Resin-based Materials to Enamel: A Systematic Review and Meta-Analysis of In Vitro Studies

PURPOSE

To systematically review the literature to evaluate whether the bond strength of resin-based materials to enamel is affected by deproteinizing agents.

MATERIALS AND METHODS

This systematic review and meta-analysis was conducted according to the PRISMA statement. PubMed, ISI Web of Science, Cochrane Library, SciELO, Scopus, LILACS, IBECS, and BVS databases were screened up to December 2020. Eligibility criteria included in vitro studies that reported the effect of a deproteinizing agent applied before or after acid etching on the immediate or long-term bond strength of resin-based materials to enamel. The meta-analysis was carried out using Review Manager (version 5.3.5). A global comparison was performed with the standardized mean difference based on random-effect models at a significance level of α = 0.05.

RESULTS

A total of 23 studies were included in the meta-analysis. In all the studies, only the immediate bond strength was evaluated. The bond strength of the materials was improved by the application of NaOCl or papain prior to enamel etching with phosphoric acid (p ≤ 0.006). None of the deproteinizing agents had a significant effect when applied after etching with phosphoric acid (p ≥ 0.27).

CONCLUSIONS

Based on in vitro studies, deproteinization with sodium hypochlorite or papain-based agents increases the immediate bond strength of resin-based materials to enamel only when used prior to phosphoric-acid etching.

Establishment of a HPLC-MS/MS Detection Method for Glyphosate, Glufosinate-Ammonium, and Aminomethyl Phosphoric Acid in Tea and Its Use for Risk Exposure Assessment

The tea shrub is grown in long-standing orchards, an environment that is suitable for persistent weed growth, which is increasingly controlled by herbicides. Therefore, there is increasing concern that tea consumers may be exposed to herbicide residues. In this study, the levels of glufosinate-ammonium (GLU), glyphosate [N-(phosphonomethyl) glycine; PMG], and its metabolite aminomethyl phosphoric acid (AMPA) were determined in tea samples by HPLC-MS/MS using several current purification methods and a new method that we developed herein. The matrix effect of our proposed method was between -27.3 and 27.7%, which was lower than that in other methods, indicating that this method effectively reduced the interference of tea matrix in the mass spectrometry process. This method was used to determine the levels of PMG, GLU, and AMPA in 780 samples, including six traditional Chinese teas (green tea, black tea, oolong tea, dark tea, white tea, and yellow tea) and a floral tea, from 14 provinces of China. Probability estimates showed that the 95th percentile risk entropy values of the three pesticide residues were far below the acceptable risk level. The risk assessment results showed that exposure to PMG, GLU, and AMPA caused by drinking tea beverages poses no significant risk to human health.

Remediation of arsenic-cationic metals from smelter contaminated soil by washings of Na2EDTA and phosphoric acid: removal efficiencies and mineral transformation

Sequential and combined soil washing tests of Na₂EDTA and phosphoric acids were conducted to remediation soil contaminated with arsenic and cationic metals (cadmium, copper, and lead) at a former metal smelter. The aim of the testing was to improve the heavy metals removal efficiency and investigate the mechanism of the influence of soil minerals on washing efficiency, including the influence on soil mineral, metal oxides, and functional groups of soil surface. The results indicated that the combined washing of Na₂EDTA and phosphoric acid was effective in removing both arsenic and cationic metals from contaminated soil and had synergy effect for most target metals. The results of metal removal efficiency indicated that the washing agent, washing mode, and washing times influenced the removal efficiencies of arsenic and cationic metals. The spectroscopic analysis demonstrated that sequential and combined washings were effective in dissolving and reforming soil minerals compared with single washing. The promoted complexation, ligand exchange, desorption, and inhibition of adsorption resulted in the synergistic effect for most target metals under combined washing.

Sorption of U(VI), Mn (II), Cu(II), Zn(II), and Cd(II) from multi-component phosphoric acid solutions using MARATHON C resin

Crude phosphoric acid is a vital component used in making phosphate fertilizers. Depending on the processes used in producing the crude phosphoric acid, it usually contains organic and inorganic contaminants. To make environmentally friendly phosphate fertilizers, these contaminants must be removed from the crude phosphoric acid stock used in making fertilizers. In this paper, commercially available strong cation exchange resin, Marathon C, was used to study the adsorptive removal of U(IV), Mn(II), Cd(II), Zn(II), and Cu(II) from synthetic multi-component phosphoric acid solutions and commercial crude phosphoric acid. Important parameters on the adsorption process such as the effects of contact time, initial metal ion concentration, sorbent dose, and concentration of phosphoric acid were investigated. The results suggested that the adsorption process reached equilibrium within 240 min for the five metal ions studied and the resin had adsorptive affinity for the metal ions in the order of U(IV) > Zn(II) > Cu(II) > Mn(II) > Cd(II). The results from the kinetics and isotherm models from the studies are very consistent with pseudo-second-order kinetic and Langmuir isotherm models. Simultaneous adsorptive removal of metal ions from the crude phosphoric acid strongly suggests that the Marathon C resin could be used in removing toxic metal ions from crude phosphoric acids used in making phosphate fertilizer.

Preparation, characterization, and efficient chromium (VI) adsorption of phosphoric acid activated carbon from furfural residue: an industrial waste

Furfural residue (FR) is an inevitable by-product of industrial furfural production. If FR is not managed properly, it will result in environmental problems. In this study, FR was used as a novel precursor for activated carbon (AC) production by H₃PO₄ activation under different conditions. Under optimum conditions, the prepared FRAC had high BET surface area (1,316.7 m²/g) and micro-mesoporous structures. The prepared FRAC was then used for the adsorption of Cr(VI). The effect of solution pH, contact time, initial Cr(VI) concentration, and temperature was systematically studied. Characterization of the adsorption process indicated that the experimental data were well-fitted by the Langmuir isotherm model and pseudo-second-order kinetics model. The maximum adsorption capacity of 454.6 mg/g was achieved at pH 2.0, which was highly comparable to the other ACs reported in the literatures. The preparation of FRAC using H₃PO₄ activation can make use of FR's characteristic acidity, which could make it preferable in practical industrial production.

Preparation and characterization of activated carbon developed from cotton cloth residue activated with phosphoric acid: adsorption of clofibric acid

Cotton cloth waste was used as a precursor to prepare activated carbon (ACCs) chemically activated with phosphoric acid. Adsorption behavior of prepared ACCs was correlated with physicochemical proprieties. The pore volume and BET surface of ACCs were determined by nitrogen adsorption isotherms and scanning electron microscopy was used to observe their surface morphologies. Fourier transform infrared (FTIR) spectroscopy analysis and pH point zero charge (pH_PZC) were conducted to determine chemical properties. Under the optimal conditions: 50% impregnation ratio and thermal treatment under N₂ flow at 600 °C during 60 min, the activated carbon prepared exhibits a high surface area 1,150 m²/g, 0.501 cm³/g micropore volume and an excellent adsorption performance. The adsorbed amount of clofibric acid is found to be 9.98 and 83 mg/g at, respectively, initial CA concentration of 10 and 100 mg/L at pH 3.0 and 20 °C. Diffusion and chemisorption are the steps controlling the adsorption of CA onto ACC 50% and the equilibrium data were well described by Freundlich isotherm.

Enhanced adsorption of copper ions by phosphoric acid-modified Paeonia ostii seed coats

Novel adsorbent, phosphoric acid-modified Paeonia ostii seed coats (PA-PSC) were successfully prepared by low-temperature pyrolysis to effectively remove Cu(II) from aqueous solution. The results revealed that equilibrium adsorption capacity (q_e) of PA-PSC for Cu(II) was notably enhanced up to 4-folds compared with the raw PSC. FT-IR and XPS analyses suggested that the adsorption of Cu(II) by PA-PSC was primarily ascribed to electrostatic forces and complexing effects. Besides, equilibrium and kinetic studies demonstrated that Freundlich and pseudo-second-order models were the actually fairly good approximations of Cu(II) adsorption. Thermodynamic analysis revealed that the adsorption of Cu(II) onto PA-PSC was a chemical, endothermic, and spontaneous process. Lastly, reusability study further confirmed the applicability of PA-PSC as a promising adsorbent for removing Cu(II) from aqueous solution.

Effect of settling time on the adsorption of 137Cs onto AMP in the AMP-coprecipitation method

Ten sets of experiments with different settling times were conducted to investigate the effect of settling time on the adsorption of ¹³⁷Cs in seawater onto ammonium phosphomolybdate (AMP). The weight yields of AMP and ¹³⁷Cs yields in all groups were generally higher than 90%. The average weight yields of AMP in each group varied from 91.8 ± 0.5 to 95.9 ± 0.6% (1 SD), and the average ¹³⁷Cs yields in each group varied from 88.3 ± 3.0 to 97.8 ± 3.7% (1 SD). The results showed that equilibrium between Cs and AMP is established immediately after the addition of stable Cs carrier and AMP, implying that the solution could be filtered immediately after the coprecipitation forms. IAEA seawater proficiency test exercises also confirmed that the AMP precipitate does not need to be treated statically in the case of 2 g AMP and 3.7 mg Cs carrier in a seawater sample solution. The modified AMP preconcentration method simultaneously meets the requirements of routine and nuclear emergency monitoring of ¹³⁷Cs in seawater.

Nitrogen-deficient g-C3Nx/POMs porous nanosheets with P-N heterojunctions capable of the efficient photocatalytic degradation of ciprofloxacin

The direct shedding of piperazine rings is critical for the degradation of antibiotic persistent organic pollutants. In this work, nitrogen-deficient g-C₃N₄ loaded with polyoxometalates porous photocatalysts with P-N heterojunctions were carried out through the formation of chemical bonds between the nitrogen-deficient C⁺ in g-C₃N_x and the bridging oxygen in polyoxometalates (POMs), including phosphomolybdic acid (PMA), phosphotungstic acid (PTA) and silicotungstic acid (STA). The adsorption and photocatalysis experiments confirm the ability of the g-C₃N_x/POMs nanosheets to efficiently remove ciprofloxacin via the synergistic effects of adsorption and photo-catalysis. Approximately, g-C₃N_x/POMs-30 exhibits the optimal degradation ability, and the degradation rates of g-C₃N_x/PMA-30, g-C₃N_x/PTA-30 and g-C₃N_x/STA-30 could respectively reach 93.1%, 97.4% and 95.6% within only 5 min under visible light. The free radical scavenging experiment and ESR free radical capture experiments confirm that ·OH and ·O₂^- are free radicals that effectively degrade CIP. According to the results of the LC-MS analysis, the intermediates produced after CIP degradation and the efficient degradation pathway are proposed. The direct shedding of piperazine rings in the decarboxylation and defluorination process leads to the most efficient degradation of CIP into the small molecules.

Does Etching of the Enamel with the Rubbing Technique Promote the Bond Strength of a Universal Adhesive System?

AIM

The aim of this in vitro research was to study the effect of etching by phosphoric acid with rubbing technique on the shear bond strength (SBS) of adhesive universal to enamel.

MATERIALS AND METHODS

Sixty extracted teeth were obtained. Three application methods (self-etch, etch-and-rinse, and etch-and-rinse with rubbing technique) were performed to bond the enamel surfaces by a universal adhesive. After 24 hours of immersion in water at 37°C, the specimens were prepared for the SBS test. Scanning electron microscopy was performed to observe the adhesive-enamel interfaces. Optical numeric microscope was used to observe the failure style. Statistical analyses were done with one-way analysis of variance test.

RESULTS

Statistically significant higher bond strength values were observed for etch-and-rinse mode with rubbing technique (25.98 ± 5.70) MPa then for the etch-and-rinse without rubbing (22.07 ± 5.27) MPa and self-etch modes (9.96 ± 2.98) MPa.

CONCLUSION

Enamel etched by 37% phosphoric acid with rubbing technique for 20 seconds showed an increase in the SBS of the universal adhesive to enamel surfaces. The tags of the adhesive can be presented more efficiently by rubbing the acid before the bonding process, consequently, an optimal interface for the bonding.

CLINICAL SIGNIFICANCE

According to the results of this in vitro study, the selective enamel etching mode with rubbing technique is advisable when using the universal adhesive, as it significantly increased the bond strength of this adhesive to enamel surfaces. The clinician should etch the enamel using phosphoric acid with rubbing technique for 20 seconds to promote the bond strength of the universal adhesive system.

Cadmium and iron removal from phosphoric acid using commercial resins for purification purpose

Three commercial resins bearing sulfonic, amino phosphonic, or phosphonic/sulfonic reactive groups have been tested for the removal of iron and cadmium from phosphoric acid solutions. The sorption properties are compared for different experimental conditions such as sorbent dosage (0.5-2.5 g L-1), phosphoric acid concentration (from bi-component solutions, 0.25-2 M), and metal concentrations (i.e., in the range 0.27-2.7 mmol Cd L-1 and 0.54 mmol Fe L-1) with a special attention paid to the impact of the type of reactive groups held on the resins. The sulfonic-based resin (MTC1600H) is more selective for Cd (against Fe), especially at high phosphoric acid concentration and low sorbent dosage, while MTS9500 (aminophosphonic resin) is more selective for Fe removal (regardless of acid concentration and sorbent dosage). Equilibrium is reached within 2-4 h. The resins can be ranked in terms of cumulative sorption capacities according the series: MTC1600H > MTS9570 > MTS 9500. Sulfuric acid (0.5-1 M) can be efficiently used for the desorption of both iron and cadmium for MTC1600H, while for MTS9570 (phosphonic/sulfonic resin) sulfuric acid correctly desorbs Cd (above 96% at 1 M concentration), contrary to Fe (less than 30%). The aminophosphonic resin shows much poorer efficiency in terms of desorption. The sulfonic resin (i.e., MTC1600H) shows much higher sorption capacity, better selectivity, comparable uptake kinetics (about 2 h equilibrium time), and better metal desorption ability (higher than 98% with 1 M acid concentration, regardless of the type of acid). This conclusion is confirmed by the comparison of removal properties in the treatment of different types of industrial phosphoric acid solutions (crude, and pre-treated H3PO4 solutions). The three resins are inefficient for the treatment of crude phosphoric acid, and activated charcoal pre-treatment (MTC1600H reduced cadmium content by 77%). However, MTC1600H allows removing over 93% of Fe and Cd for H3PO4 pre-treated by TBP solvent extraction, while the others show much lower efficiencies (< 53%).

Effect of Soil Washing Solutions on Simultaneous Removal of Heavy Metals and Arsenic from Contaminated Soil

In this study, we investigated the feasibility of using a solution of sulfuric acid and phosphoric acid as an extraction method for soil-washing to remove Cu, Pb, Zn, and As from contaminated soil. We treated various soil particles, including seven fraction sizes, using sulfuric acid. In addition, to improve Cu, Pb, Zn, and As removal efficiencies, washing agents were compared through batch experiments. The results showed that each agent behaved differently when reacting with heavy metals (Cu, Pb, and Zn) and As. Sulfuric acid was more effective in extracting heavy metals than in extracting As. However, phosphoric acid was not effective in extracting heavy metals. Compared with each inorganic acid, As removal from soil by washing agents increased in the order of sulfuric acid (35.81%) < phosphoric acid (62.96%). Therefore, an enhanced mixture solution using sulfuric acid and phosphoric acid to simultaneously remove heavy metals and As from contaminated soils was investigated. Sulfuric acid at 0.6 M was adopted to combine with 0.6 M phosphoric acid to obtain the mixture solution (1:1) that was used to determine the effect for the simultaneous removal of both heavy metals and As from the contaminated soil. The removal efficiencies of As, Cu, Pb, and Zn were 70.5%, 79.6%, 80.1%, and 71.2%, respectively. The combination of sulfuric acid with phosphoric acid increased the overall As and heavy metal extraction efficiencies from the contaminated soil samples. With the combined effect of dissolving oxides and ion exchange under combined washings, the removal efficiencies of heavy metals and As were higher than those of single washings.

Significant Enhancement of Gaseous Elemental Mercury Recovery from Coal-Fired Flue Gas by Phosphomolybdic Acid Grafting on Sulfurated γ-Fe2O3: Performance and Mechanism

The existing technologies to control Hg emissions from coal-fired power plants can be improved to achieve the centralized control of Hg⁰ emissions, which continue to pose a risk of Hg exposure to human populations. In this work, MoS_x@γ-Fe₂O₃, formed by the sulfuration of phosphomolybdic acid (HPMo)-grafted γ-Fe₂O₃, was developed as a magnetic and regenerable sorbent to recover gaseous Hg⁰ from coal-fired flue gas as a cobenefit to the use of wet electrostatic precipitators. The thermal stability of γ-Fe₂O₃ was notably enhanced by HPMo grafting; thus, the magnetization of MoS_x@γ-Fe₂O₃ hardly decreased during the application. The kinetic analysis indicates that the chemical adsorption of gaseous Hg⁰ was mainly dependent on the amounts of surface S₂^2- and surface adsorption sites. Although the amount of S₂^2- on sulfurated γ-Fe₂O₃ decreased after HPMo grafting, the amount of surface adsorption sites significantly increased due to the formation of a layered MoS_x structure on the surface. Therefore, the ability of sulfurated γ-Fe₂O₃ to capture Hg⁰ was improved considerably after HPMo grafting. Furthermore, low concentrations of gaseous Hg⁰ in coal-fired flue gas can be gradually enriched by at least 1000 times by MoS_x@γ-Fe₂O₃, which facilitates the recovery and centralized control of gaseous Hg⁰ in flue gas.

Batch interaction of emerging tetracycline contaminant with novel phosphoric acid activated corn straw porous carbon: Adsorption rate and nature of mechanism

In this work, corn straw (CS) based porous carbon was prepared by one-step phosphoric acid (H₃PO₄) low temperature activation. The impregnation ratios (H₃PO₄/CS, g/g) played an important role in the pore development. ACS_300-1 engineered at 300 °C and the impregnation ratio of 1.0 showed the maximal specific surface area of 463.89 m²/g with total pore volume of 0.387 cm³/g, attaining a high tetracycline (TC) uptake of 227.3 mg/g. The adsorption of TC onto ACS_300-1 was found tolerant with wide pH (2.0-10.0) and high ionic strength (0 - 0.5 M). The adsorption data can be fitted well by the pseudo-second order kinetic model and Langmuir isotherm model. The endothermic and spontaneous properties of the adsorption system was implied by Thermodynamic study. The findings of the current work conclude that one-step H₃PO₄ activation is a green and promising method for corn straw based porous carbon that may be found with great potentials in antibiotic containing wastewater treatment.

Towards establishing indicative values for metabolites of organophosphate ester contaminants in human urine

In 2015, nine laboratories from Belgium, USA, Canada, China, and Australia participated in an interlaboratory exercise to quantify metabolites of organophosphate ester (OPE) contaminants in pooled human urine. Pooled human urine available as SRM 3673 (Organic contaminants in non-smokers' urine) was obtained from the U.S. National Institute of Standards and Technology and was analyzed for its content of OPE metabolites. Each participating laboratory received 10 mL sample and used its own validated method and standards to report the concentrations of the OPE metabolites of its choice. Four OPE metabolites were consistently measured by most laboratories and they were the following diesters: bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), diphenyl phosphate (DPHP), bis(2-chloroethyl) phosphate (BCEP), and bis(1-chloro-2-propyl) phosphate (BCIPP). Concentrations of other OPE metabolites in SRM 3673 were also reported but are only considered as informative values since they were measured by three laboratories at most. All laboratories used liquid chromatography with tandem mass spectrometry (LC-MS/MS) with or without solid-phase extraction (SPE). This is the first study to report indicative values for OPE metabolites in a human urine Standard Reference Material. It is expected that these indicative values obtained for these four metabolites will be used as quality control to ensure compatibility of results in biomonitoring studies and by other researchers who validate their own methods for the quantification of OPE metabolites in human urine.