Adsorption Of Phosphoric Acid Research Articles

Precise Construction of the Triple-Phase Boundary and Its Antiphosphate Poisoning Effect in the Confined Region.

As a critical component for the oxygen reduction reaction (ORR), platinum (Pt) catalysts exhibit promising catalytic performance in High-temperature-proton exchange membrane fuel cells (HT-PEMFCs). Despite their success, HT-PEMFCs primarily utilize phosphoric acid-doped polybenzimidazole (PA-PBI) as the proton exchange membrane, and the phosphoric acid within the PBI matrix tends to leach onto the Pt-based layers, easily causing toxicity. Herein, we first propose UiO-66@Pt3Co1-T composites with precisely engineered interfacial structures. The UiO-66@Pt3Co1-T exhibits an octahedral porous framework with uniform structural dimensions and even distribution of surface nanoparticles, which demonstrate superior ORR performance compared to commercial Pt/C. The unique structure and morphology of the composites also exhibit a favorable half-wave potential in different concentrations of phosphoric acid electrolyte, regulated by the phosphoric acid adsorption site and intensity.This finding suggests that the incorporation of Co could effectively modulate the Pt d-band center, thereby enhancing the ORR performance. Furthermore, the selective adsorption of phosphoric acid by ZrO2 enables precise control over the phosphoric acid distribution. Notably, the retention of the octahedral framework post high-temperature treatment facilitates the establishment of dual transport pathways for gases and protons, leading to a stable and efficient triple-phase boundary.

Improving the performance and long-term durability of high-temperature PEMFCs: A polyvinylpyrrolidone grafting modification strategy of polybenzimidazole membrane

This study introduces an innovative approach to graft Polyvinylpyrrolidone (PVP) onto Polybenzimidazole (PBI) to synthesise Proton Exchange Membranes (PEMs) with high performance and durability. As a widely used hydrophilic polymer in industry, PVP can add numerous nitrogen-containing functional groups to the membrane to enhance its phosphoric acid (PA) binding ability. In this work, Polybenzimidazole-graft-polyvinylpyrrolidone (PVP-g-PBI) polymers with varying grafting degrees were synthesized and tested to investigate the impact of the grafting modification on the membrane's proton conductivity, thermal properties, and electrochemical performance. With the introduction of PVP side chains, the fuel cell showed enhanced PA uptake and substantial improvements in peak power density. Notably, PBI-g-PVP membranes with a grafting degree of 22.4 % achieved a peak power density enhancement up to 1312 mW cm⁻2 at 160 °C, a 59.6 % increase over pristine PBI membranes. Due to the increased PA binding sites in the membrane, the PBI-g-PVP PEMs exhibit better PA adsorption ability and long-term durability than pristine membranes. The accelerated stress test (AST) demonstrated that the PBI-g-PVP membranes maintain a peak power density of 1105 mW cm⁻2 after a 70-h test, equivalent to 183.9 % of the pristine PBI membrane. The improved fuel cell performance and durability of PBI-g-PVP PEMs underscore the potential of this grafting strategy.

Lanthanum hydroxide showed best application potential in La-based materials based on its stable phosphate adsorption properties in complex water environments

Three lanthanum morphology materials encompassing all lanthanum composites were synthesized by the direct precipitation method, and their phosphate adsorption order was determined as La2(CO3)3 > La(OH)3 > La2O3. Further comparison of the adsorption performance between La2(CO3)3 and La(OH)3 revealed that the former exhibited a twofold higher rate of adsorption compared to the latter. The presence of SO42−, HCO3−, Mg2+, and HA in the water led to a decrease in the phosphate adsorption of La2(CO3)3 and La(OH)3, while Ca2+ enhances the adsorption of phosphoric acid by both materials. Compared to La2(CO3)3, La(OH)3 exhibited stronger resistance against coexisting ions. The pH was the limiting factor for phosphate adsorption in both cases, and their adsorption capacity decreased significantly as the pH increased. The phosphate adsorption mechanism of La2(CO3)3 was ligand exchange to form inner-sphere complexes, while the phosphate adsorption mechanism of La(OH)3 involved ligand exchange, inner-sphere complexation, and electrostatic attraction. The stability of La(OH)3 exhibited superior performance compared to that of La2(CO3)3 over 5 adsorption-desorption cycles. Although La2(CO3)3 had a higher initial phosphate adsorption capacity than La(OH)3, its phosphate adsorption capacity decreased by 40% after five adsorption-desorption cycles, while that of La(OH)3 decreased by 2.3%. Additionally, the amount of La(OH)3 adsorbed after five cycles was 25.6% higher than that of La2(CO3)3. Therefore, La(OH)3 performs better regeneration adsorption than La2(CO3)3. Furthermore, a smaller dosage of La(OH)3 was required compared to La2(CO3)3 in a test aimed at lowering the actual phosphate concentration in water to 0.5 mg/L. In summary, La(OH)3 is a more suitable substrate for cyclic adsorption for phosphorus removal than La2(CO3)3 and has better potential for practical application. In conclusion, La(OH)3 proves to be a more suitable substrate for cyclic adsorption in phosphorus removal compared to La2(CO3)3 and exhibits superior potential for practical application.

Tetramethyl poly(aryl ether ketone) modified by DABCO cationic polymer for high temperature proton exchange membrane fuel cells

Rationally constructing proton transport channel within high temperature proton exchange membranes (HT-PEMs) plays a critical role in lowering the mass transfer resistance and thus improving the performance of HT-PEM fuel cells (HT-PEMFCs). We herein designed a microphase-separated structure to promote proton transmitting by incorporating 1,4-Diazabicyclo[2.2.2]octane (DABCO) cationic polymer into tetramethyl poly(aryl ether ketone) (TMPAEK). The flexible and cationic segments afforded a polarity difference from TMPAEK, resulting in easier phosphoric acid adsorption. High proton conductivity of 135 mS cm−1 was obtained under anhydrous conditions at 150 °C. Besides, the hydrophilic domains that containing N-heterocycle could stabilize phosphoric acid through hydrogen bonding interactions, resulting in high phosphoric acid retention of ∼80 % after 288 h test. A Peak power density of 496 mW cm−2 was achieved in non-humidified H2/O2 without back pressure at 140 °C, which was higher than that of m-PBI under the same conditions. This work not only paved a way to tailor the ion conductivity of membrane, but also provided a highly competitive membrane for HT-PEMFCs.

Facile synthesis of Fe-doped ZIF-8 and its adsorption of phosphate from water: Performance and mechanism.

To remove phosphate from water, a novel Fe-doped ZIF-8 was synthesized as a superior adsorbent. The Fe-doped ZIF-8 was fully characterized using different characterization techniques and it was found that the as-prepared Fe-doped ZIF-8 (denoted as ZIF-(2Zn:1Fe)) showed a polyhedral morphology with a large specific surface area of 157.64 m2/g and an average pore size of 3.055 nm. Analyses using Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction showed that Fe atoms were successfully incorporated into the ZIF-8 skeleton. Batch experiments demonstrated that the molar ratio of Fe and Zn has effects on phosphate adsorption. The adsorption kinetics conformed to a pseudo-second-order model with a high correlation coefficient (R2 = 0.9983). The adsorption isotherm matched the Langmuir model (R2 = 0.9994) better than the Freundlich model (R2 = 0.7501), suggesting that the adsorption of phosphoric acid by ZIF-(2Zn:1Fe) can be classified as a chemisorption on a homogeneous surface. The adsorption amount was 38.60 mg/g. It was found that acidic environments favored the adsorption reaction and the best adsorption was achieved at an initial pH of 2. Inhibition of adsorption by common anions is NO3-> CO32-> SO42-> Cl-. Characterization results indicate that the main mechanism of adsorption is surface complexation interactions.

The role of anions for phosphoric acid uptake behaviors and electrochemical performance of ion-pair type high-temperature polymer electrolyte membranes

Quaternized ion-pair membranes have high phosphoric acid (PA) uptake and retention due to strong interaction energy between quaternary ammonium with PA. However, there is currently a lack of clear understanding of the role of anions on the PA uptake behaviors and mechanism of ion-pair type membranes. In this work, the PA uptake behaviors of quaternized poly (terphenyl piperidinium) (QAPTP-X, X represents anions) with four kinds of anions (Cl−, OH−, HCO3− and H2PO4−) were investigated. Due to the neutralization reaction between PA and OH−/HCO3−, QAPTP-OH− and QAPTP-HCO3− membranes show a faster PA adsorption rate (PA uptake for 2 min: 116 wt% of QAPTP-OH−≈109 wt% of QAPTP-HCO3− >95 wt% of QAPTP-H2PO4− ≫64 wt% of QAPTP-Cl−). Besides, the Pt catalyst is poisoned by strong adsorption anions Cl− migrated from the QAPTP-Cl− membrane, which leads to sluggish electrode reaction kinetics and lower peak density. Therefore, a new perspective is provided for studying the mechanism of PA uptake and electrochemical performance for ion-pair type membranes.

Low Pt loading for high-performance fuel cell electrodes enabled by hydrogen-bonding microporous polymer binders.

A key challenge for fuel cells based on phosphoric acid doped polybenzimidazole membranes is the high Pt loading, which is required due to the low electrode performance owing to the poor mass transport and severe Pt poisoning via acid absorption on the Pt surface. Herein, these issues are well addressed by design and synthesis of effective catalyst binders based on polymers of intrinsic microporosity (PIMs) with strong hydrogen-bonding functionalities which improve phosphoric acid binding energy, and thus preferably uphold phosphoric acid in the vicinity of Pt catalyst particles to mitigate the adsorption of phosphoric acid on the Pt surface. With combination of the highly mass transport microporosity, strong hydrogen-bonds and high phosphoric acid binding energy, the tetrazole functionalized PIM binder enables an H2-O2 cell to reach a high Pt-mass specific peak power density of 3.8 W mgPt-1 at 160 °C with a low Pt loading of only 0.15 mgPt cm-2.

Study of Pt Alloy Catalysts for Oxygen Reduction Reaction on Rde and in MEA for High-Temperature Pemfcs

High-temperature polymer electrolyte fuel cells (HT-PEMFCs) have advantages in enhanced fuel impurities tolerance, easier heat rejection, and simpler water management[1]. Low-temperature PEMFCs with perfluorosulfonic acid electrolytes (e.g., Nafion) could not provide sufficient proton conductivity in the absence of water when T > 120 °C, limiting the application when a higher temperature is desired. High-temperature (HT-) PEMFCs have been developed by using phosphoric acid (H3PO4)-doped polymer electrolyte (e.g., polybenzimidazole, quaternary ammonium biphosphate ion pair coordinated polyphenylene, etc.) [2-4], where H3PO4 can conduct proton at high temperature up to 200 °C. Such change of the reaction environment, however, also affects oxygen reduction reaction (ORR) kinetics. Despite of a facilitated reaction kinetics under high temperature, a high Pt loading is still demanded in state-of-the-art HT-PEMFCs. To enhance ORR activity and increase Pt utilization, here we employ a strategy to alloy Pt with another transition metal (M), which has been demonstrated to be effective in LT-PEMFCs. In this study, Pt and Pt-M catalysts were used to investigate the alloy effect on the adsorption strength of H3PO4 and ORR in both half-cell rotating disk electrode (RDE) and membrane electrode assembly (MEA). In RDE study, the competition adsorption of phosphoric acid has led to a suppression on ORR activity on all catalysts, with less impact on ORR at 160 °C using pure H3PO4 than RT using 1 M H3PO4. Since alloying not just affects the O binding energy, but also H3PO4 adsorption, a different trend of ORR on Pt-M alloy catalysts was resulted in the presence of H3PO4. The alloy effect was further studied in MEA at 160 °C, which also indicates the effectiveness of using HT-RDE setup for HT-ORR catalyst screening. Reference: [1] Gittleman, C. S.; Jia, H.; De Castro, E. S.; Chisholm, C. R. I.; Kim, Y. S. Proton Conductors for Heavy-Duty Vehicle Fuel Cells. Joule 2021, 5 (7), 1660–1677.[2] Pingitore, A. T.; Huang, F.; Qian, G.; Benicewicz, B. C. Durable High Polymer Content m/ p-Polybenzimidazole Membranes for Extended Lifetime Electrochemical Devices. ACS Appl. Energy Mater. 2019, 2 (3), 1720–1726.[3] Lee, K. S.; Spendelow, J. S.; Choe, Y. K.; Fujimoto, C.; Kim, Y. S. An Operationally Flexible Fuel Cell Based on Quaternary Ammonium-Biphosphate Ion Pairs. Nat. Energy 2016, 1 (9).[4] Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated Phosphonic Acid Electrodes for High Power Heavy-Duty Vehicle Fuel Cells. Nat. Energy 2022, 7 (3), 248–259.

Hydrothermal in situ synthesis of high-crystallinity layered double hydroxide on electrospun polyacrylonitrile non-woven membrane: Application as anion capture filter

Layered double hydroxide (LDH) crystals were grown in the presence of polyacrylonitrile (PAN) nanofibers to develop a three-dimensionally-structured hybrid filter with high anion adsorption performance. The tensile strength and chemical resistance of the PAN nanofibers manufactured by electrospinning were improved upon heat treatment at 250 °C for 60 min. The growth of LDH on PAN was conducted by hydrolysis using urea or hexamethylenetetramine (HMT), and optimum conditions for this “in situ synthesis” were investigated. As a result, LDH plate-like crystals with a lateral size of ~20 μm were obtained by hydrothermal treatment at 140 °C for 24 h using HMT. The crystals grew densely perpendicular to the surface of the PAN fibers. After converting the LDH grown on the fiber fabric to LDH contain Cl− in the interlayer, the resulting fabric was set in a filter holder and a phosphoric acid adsorption test was conducted. The results showed that the hybrid filter prepared by this in situ hydrothermal synthesis had good phosphate adsorption characteristics, and that small amounts of phosphate ions were adsorbed selectively from water containing competing sulfate ions.

Highly conductive quaternary ammonium-containing cross-linked poly(vinyl pyrrolidone) for high-temperature PEM fuel cells with high-performance

Poly(vinyl pyrrolidone) (PVP)-based high-temperature polymer electrolyte membranes (HT-PEMs) doped with phosphoric acid (PA) present an attractive prospect for high-temperature fuel cell. However, its proton conductivities and mechanical properties are inversely dependent on PVP content in membranes. Herein, chloromethyl-polysulfone is used as a polymeric crosslinker to fabricate cross-linked PVP. The effects of chloromethylation degree of polysulfone on PVP cross-linking degree, free volume and other parameters are studied. The quaternary amine groups introduced by cross-linking reaction enhances PA adsorption and retention capacity of membrane. The increased molar free volume created by polymeric crosslinker can accommodate more PA storage and reduce the polymer main chain plasticization. Thus, the mechanical properties of membranes are maintained. When compared to uncross-linked C-PVP-0/PA, the cross-linked C-PVP-13.7%/PA exhibits improved mechanical strength with increasement of 140% (4.5 MPa) and enhanced proton conductivity with increasement of 119% (120.0 mS cm−1@160 °C). Also, these superior characteristics allow a significantly enhanced H2–O2 fuel cell performance with the membrane of 724.9 mW cm−2 @160 °C, which has increasement of 50% in comparison with that of the C-PVP-0%/PA membrane, and excellent durability. These praiseworthy results suggest that the cross-linked membrane within moderately molar free volume is potential to act as HT-PEMs materials for real-world applications.

Theoretical analysis of the adsorption of phosphoric acid and model phosphate monoesters on CeO2(111)

Ceria has been shown to catalyze the dephosphorylation of phosphate monoesters at ambient temperature. As a step toward understanding the reaction mechanism on ceria, first-principles density functional theory calculations in the GGA-PW91+U approach have been carried out to study the adsorption of phosphoric acid and two model phosphate monoesters, methyl phosphate and para-nitrophenyl phosphate, on CeO2(111). Consistent patterns are found in terms of energetic, structural, electronic, and vibrational properties upon adsorption. For the parent molecules, bonding of the phosphorous atom directly to a surface lattice oxygen atom (Olatt) is the only stable molecular adsorption state. Common entities that reduce Ce4+ to Ce3+ (e.g., co-adsorbed H atom, surface and subsurface oxygen vacancy) mildly perturb the P-Olatt bond, but Ce3+ by itself has only a negligible effect. Deprotonation is exothermic for all three phosphate species on CeO2(111), much more so if they are adsorbed in an oxygen vacancy via a phosphoryl O than on a stoichiometric surface. Infrared spectra have been simulated for the adsorbed states of the model phosphates for comparison with future experiments.

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.

Excess adsorption of phosphoric acid from extremely acidic solutions by covalent organic framework EB-COF:Br

The industrial waste streams with excess phosphorus acid (H3PO4) was generated in semiconductor industries that has extremely low pH rendering commercial adsorbents unfit for adsorption recycling of valuable materials. This study for the first time use covalent organic framework EB-COF:Br to adsorb phosphoric acid from extremely acidic H3PO4 solutions at pH ranging 0.86 to −0.65. The EB-COF:Br could maintain structural stability with these extremely acidic solutions. At 25 °C, 95% adsorption could be completed within 10 min of contact; while the adsorption capacities of EB-COF:Br from 75% H3PO4 solution ranged 6520‒6980 mg-H3PO4/g during 25–45 °C. The adsorption is regarded isoenthalpic with no heat effects. Water washing is efficient for H3PO4 desorption, and the washed COF can be reused as an efficient adsorbent under extremely acidic environment. The interactions between (‒N+=) and (‒CO) groups, and part of the (‒NH‒) groups participated in the adsorption process with adsorbed H3PO4 molecules. The adsorbed H3PO4 molecules then formed H-bonding to trap the excess free H3PO4 molecules to the internal cavity of the COF.

High Temperature Polymer Electrolyte Membrane Achieved By Grafting Poly(1-vinylimidazole) on Polysulfone for Fuel Cell Applications

High temperature polymer electrolyte membranes with phosphoric acid doping are crucial materials of high temperature fuel cells. However, the evolution of the type membrane is suffering from the trade-off between proton conductivity and mechanical strength, because high proton conductivity requires high phosphoric acid doping level, which will reduce the mechanical properties due to the plasticization of phosphoric acid on polymer backbone. Here, a new strategy is employed to respond to the unresolved challenges by grafting poly(1-vinylimidazole) as phosphoric acid doping sites on polysulfone backbone via atom transfer radical polymerization. Then poly(1-vinylimidazole) grafted polysulfone membrane with different length of side chains is obtained and soaked in phosphoric acid to work as high temperature polymer electrolyte membrane. The tapping-mode AFM images and 1-D SAXS result of PA doped membrane suggest the formation of micro-phase separated structures, and the ionomer peaks shift from 1.34 nm-1 to 1.19 nm-1 with increasing the length of side chain, corresponding to d-spacing of 4.67 nm and 5.28 nm, respectively. Therefore, the prepared phosphoric acid doped membranes possess excellent proton conductivity of 127 mS cm-1 under 160 °C due to the structure, while mechanical properties are retained due to the reduction of plasticizing effect caused by the separation of phosphoric acid adsorption sites and polymer backbone, presenting an outstanding tensile strength of 7.94 MPa. Meanwhile, the impressive fuel cell performance with the membranes is gained, reaching a maximum peak power density of 559 mW cm-2 under 160 oC. More importantly, the work provides a new sight to solve the trade-off between proton conductivity and mechanical strength for phosphoric acid doped high temperature polymer electrolyte membranes. Figure 1

High temperature polymer electrolyte membrane achieved by grafting poly(1-vinylimidazole) on polysulfone for fuel cells application

Phosphoric acid (PA)-doped high temperature polymer electrolyte membranes (HT-PEMs) are crucial materials for HT-PEM fuel cells (HT-PEMFCs). However, the development of HT-PEMs suffers from the trade-off between proton conductivity and mechanical strength. High proton conductivity requires a high doping level of PA, and PA acts as a plasticizer that reduces the mechanical properties. Here, a new strategy is employed to address the unresolved challenges; the strategy is to graft poly(1-vinylimidazole) as PA doping sites on the polysulfone backbone. This is achieved via atom transfer radical polymerization. High proton conductivity is achieved because of the formation of micro-phase separated structures, and the mechanical properties are retained because of the reduced plasticizing effect, which is caused by the separation of PA adsorption sites and the polymer backbone. The prepared PA-doped membranes have excellent proton conductivity of 127 mS cm−1 at 160 °C and outstanding tensile strength of 7.94 MPa. Meanwhile, single H2-O2 cell performance with the optimized membrane is impressive, reaching a peak power density of 559 mW cm−2 at 160 °C. More importantly, this work provides new insight into solving the trade-off between proton transport and mechanical strength for PA-doped HT-PEMs.

Polybenzimidazole/BaCe0.85Y0.15O3-δ nanocomposites with enhanced proton conductivity for high-temperature PEMFC application

The present work reports the synthesis of polybenzimidazole (PBI)/BaCe0.85Y0.15O3-δ nanocomposite membrane. The obtained membranes were investigated to use as novel electrolytes in high-temperature proton exchange fuel cells. The PBCYx membranes were prepared with dispersing BaCe0.85Y0.15O3-δ into the polyimidazole membrane by solution casting method. The obtained membranes were used as novel proton conductors. The thermal stability and structural properties were investigated. The conductivity and morphology of the obtained materials were studied using impedance spectroscopy AC (IS) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX). The maximum phosphoric acid adsorption (175%) and protonic conductivity (0.092 S/cm at 180 °C under dry conditions) were observed for all of the PBI nanocomposite membranes containing 5 wt.% of BaCe0.85Y0.15O3-δ in the membrane matrix. The polarization and power density curves were studied at 150 and 180 °C operating temperatures. The power density of about 0.42 W/cm2 and current density of about 0.84 A/cm at 0.5 V and 180 °C were achieved under dry conditions. The data obtained from our studies showed that the physicochemical properties of the novel nanocomposites were enhanced for using in the high-temperature proton transfer fuel cells.

Nutrient removal from digested swine wastewater by combining ammonia stripping with struvite precipitation.

Typical biological processing is often challenging for removing ammonia nitrogen and phosphate from swine wastewater due to inhibition of high ammonia on activity of microorganisms, exhaustion of time, and low efficiency. In this study, a physicochemical process by combining ammonia stripping with struvite precipitation has been tested to simultaneously remove ammonia nitrogen, phosphate, and chemical oxygen demand (COD) from digested swine wastewater (DSW) with high efficiency, low cost, and environmental friendliness. The pH, temperature, and magnesium content of DSW are the key factors for ammonia removal and phosphate recovery through combining stripping with struvite precipitation. MgO was used as the struvite precipitant for NH4+ and PO43- and as the pH adjusted for air stripping of residual ammonia under the condition of 40°C and 0.48m3h-1L-1 aeration rate for 3h. The results showed that the removal efficiency of ammonia, total phosphate, and COD from DSW significantly increased with increase of MgO dosage due to synergistic action of ammonia stripping and struvite precipitation. Considering the processing cost and national discharge standard for DSW, 0.75gL-1 MgO dosage was recommended using the combining technology for nutrient removal from DSW. In addition, 88.03% NH4+-N and 96.07% TP could be recovered from DSW by adsorption of phosphoric acid and precipitation of magnesium ammonium phosphate (MAP). The combined technology could effectively remove and recover the nutrients from DSW to achieve environmental protection and sustainable and renewable resource of DSW. An economic analysis showed that the combining technology for nutrient removal from DSW was feasible.

Effective adsorption of phosphoric acid by UiO-66 and UiO-66-NH2 from extremely acidic mixed waste acids: Proof of concept

Streams of waste mixed acids from conventional wet etching processes contain high levels of H3PO4, which warrant recycling. This investigation is the first to use metal organic framework UiO-66 and UiO-66-NH2 to adsorb phosphoric acid from waste mixed acids from the world's largest semiconductor foundry, a synthetic HNO3H3PO4HAc mixture, and 85% phosphoric acid. Both UiO-66 and UiO-66-NH2 have high capacities to adsorb H3PO4 in extremely acidic solutions. The Langmuir adsorption capacities (qmax’s) of UiO-66 for waste mixed acids and a synthetic HNO3H3PO4HAc mixture on UiO-66 at 25 °C are 3360 and 8,510 mg-H3PO4/g, respectively, and that of 85% phosphoric acid on UiO-66 is 4,790 mg-H3PO4/g. The qmax of UiO-66-NH2 for phosphoric acid from 25% to 75% waste mixed acids is 4550 mg-H3PO4/g, which exceeds that of UiO-66. The corresponding P:Zr ratio for adsorbed MOF is in the range 6.2‒13.5, suggesting that the tested MOF crystals are super-adsorbents of phosphoric acid under extremely acidic conditions.

Electrodeposition-fabricated PtCu-alloy cathode catalysts for high-temperature proton exchange membrane fuel cells

Pt electrocatalysts in high-temperature proton exchange membrane fuel cells (HT-PEMFCs) containing phosphoric acid (PA)-doped polymer membranes are prone to poisoning by leaked PA. We performed a preliminary density functional theory (DFT) study to investigate the relationship between the electronic structure of Pt surfaces and their adsorption of PA. Excess charge on Pt was found to weaken its bonding with the oxygen in PA, thus presenting a strategy for the fabrication of PA-resistant catalyst materials. Consequently, PtCu-alloy catalysts with various compositions were prepared by electrodeposition. The morphologies and crystalline structures of the alloys were strongly dependent on alloy composition. Moreover, the Pt atoms in the PtCu-alloy catalysts were found to be in an electron-rich state, similar to that of the excessively charged Pt simulated in the DFT study. As a result, the oxygen reduction reaction activities of the PtCu-alloy catalysts were superior to that of a Pt-only catalyst, regardless of the presence of PA. In the absence of PA, the higher activity of the PtCu-alloy catalysts was ascribable to conventional alloying effects, while the increased activity in the presence of PA was largely due to the enhanced resistance to PA poisoning. Therefore, PtCu-alloy catalysts easily prepared by electrodeposition were found to be strong candidate materials for HT-PEMFC electrodes.

Surface chemistry and flotation behavior of dolomite, monazite and bastnäsite in the presence of benzohydroxamate, sodium oleate and phosphoric acid ester collectors

Carboxylates, hydroxamates and organic phosphoric acids are typical collectors used for rare earth mineral flotation. Carboxylates are not selective, while hydroxamates, though selective, require high concentrations to recover a significant amount of rare earth minerals. Other collectors such as organic phosphoric acids, which showed promising rare earth minerals collecting potential, have recently been explored. However, the mechanism of organic phosphoric acid adsorption on the surface of rare earth minerals has not been very well investigated. In this study, zeta potential measurements were conducted to study the surface property of dolomite, monazite and bastnäsite in the presence of benzohydroxamate (hydroxamate), sodium oleate (carboxylate) and Flotinor 1682 (phosphoric acid ester). These measurements, complemented with ATR-FTIR spectroscopy, evaluated the adsorption of the collectors at the surface of the minerals. The adsorption of the collectors was found to be highly influenced by the mineral cations present at the mineral/solution interface and in the solution. Possible adsorption mechanisms are proposed and discussed; some of which agree with those presented in the literature, while others provided different perspective. Although benzohydroxamate was the most selective, potential flotation processes to recover rare earth minerals using sodium oleate and Flotinor 1682 were also suggested.