PO4 Adsorption Research Articles

Role of surface defects in trap of monoatomic polonium on Pd surface

• Strong chemisorption of Po was obtained on vacancy-defective Pd (111) and stepped Pd (211) surfaces. • Adsorption of Po on vacancy or on hcp site at step edge is more stable. • Vacancy on Pd (111) surface and step defect on Pd (211) are preferred sites for Po retention. 210 Po is a radiotoxic element and will evaporate into the cover gas above the coolant in accelerator-drive systems or lead-bismuth fast reactor. In order to prevent the build-up of Po and ensure the safety of the reactors, reliable filter systems need to be developed and Pd has been proposed as candidate filter material. To acquire fundamental knowledge of surface defects trapping monoatomic Po, adsorption and diffusion of Po on vacancy-defective Pd(111) and stepped Pd(211) surfaces have been calculated by first-principles. Strong chemisorption was obtained for Po on vacancy-defective Pd(111) and stepped Pd(211), vacancy and hcp site at step edge are preferred sites for Po adsorption. The activation energies for Po jump from vacancy on Pd(111) surface and for Po diffusion on stepped Pd(211) surface are obviously larger than that for Po diffusion on other non-vacancy sites on Pd(111) surface. The results indicate that surface defects such as vacancy and step defect are preferred sites for Po adsorption and retention.

Amine-grafted walnut shell for efficient removal of phosphate and nitrate.

The presence of emerging pollutants such as PO43- and NO3- in water bodies has attracted worldwide concern about their severe effects on water bodies and the health of humankind in general. Therefore, to preserve the health of humankind and environmental safety, it is of the essence that industrial effluents are treated before they are discharged into water bodies. Amine functionalized walnut shells (ACWNS) were synthesized, characterized, and then tested as a novel adsorbent for PO43- and NO3- removal. The effects of pH, dosage, initial phosphate concentration, interference ions, and temperature on the removal of phosphate and nitrate were investigated. Notably, the adsorption of PO43- and NO3- was exothermic and spontaneous, with a maximum uptake capacity of phosphate and nitrate, at 293K, 82.2 and 35.7mgg-1, respectively. The mechanism by which these ions were adsorbed onto ACWNS could be electrostatic interactions and hydrogen bonding. Pseudo-second-order kinetic modelfitted the PO43- and NO3- adsorption, while Freundlich and Langmuir models best fitted the PO43- and NO3- adsorption, respectively. Furthermore, in the binary system, the uptake capacity of phosphate decreased by 14.4% while nitrate witnessed a reduction in its uptake capacity of 10.4%. ACWNS has a higher attraction towards both ions and this could be attributed to the existence of a variety of active areas on ACWNS that exhibit a degree of specificity for the individual ions. Results obtained from real water sample analysis confirmed ACWNS as highly efficient to be utilized for practical remediation processes.

Characteristics of diatomite-alginate-Fe3O4 composite as a phosphate adsorbent

Technological approaches to the use of diatomaceous earth as a raw material for the creation of composite adsorbents for wastewater treatment from phosphate ions are analysed. It is shown that the developed surface of diatomite can be used to create a granular adsorbent, and iron (III) oxides (magnetite, goethite, lepidocrocite, ferrihydrite, hematite and goethite) are environmentally safe, cheap, economically feasible modifiers. Emphasis is placed on the possibility of obtaining magnetic granules due to the formation of magnetite. The use of the deposition method for the formation of the applied granular adsorbent is proposed.
 The influence of diatomite concentration on the static strength of granules was established. It is determined that the diameter of the nozzle is also an important factor. The selected technical solutions are aimed at solving the problems of granule hardening and ensuring high adsorption activity. Experimental studies of the synthesis and granulation of the composite adsorbent alginate - diatomaceous earth - magnetite have shown that an increase in the content of diatomaceous earth leads to a natural increase in the size of the granules. When increasing the diameter of the nozzle from 1.5 mm to 3.5 mm, for example, the size of the granules 1.5-4.0 (dc = 1.5 mm), 2.0-5.0 mm (dc = 3.0 mm) and 2.5-5.0 mm (dc = 3.5 mm). The diatomaceous earth content of more than 20% does not allow to carry out high-quality granulation on the experimental installation due to the increase in the viscosity of the suspension. The relationship between the size of gel granules and dried. The process of application of the active magnetic phase of the adsorbent is investigated. The dependence of the quality of the granulation process on the solid phase content is established. The measured static strength of the adsorbent granules is in the range of 17 - 25 kPa. It is established that the composite adsorbent with the applied layer of magnetite has magnetic properties. The adsorption of PO43- anions from aqueous solutions was studied. For the adsorbent alginate - diatomite and alginate - diatomite - Fe3O4 - the adsorption capacity is 4 and 9 mg PO43- / g, respectively. The obtained composite adsorbents have a set of functional properties that are promising for use in modern water purification and purification systems.

Comparison of the effects of competitive adsorption and reductive dissolution on migration of arsenic in lake sediment

ABSTRACT Arsenic-contaminated sediment of Lake Yangzonghai (Yunnan province, China) and its overlying water was used to investigate the effects of phosphate ion (PO4 3−) and microbial activity on the migration of arsenic in the sediment. The results showed that the competitive adsorption of PO4 3− was the primary factor for the release of arsenic from the sediment to the overlying water, while microbial activity played a minor role in promoting the reductive dissolution of iron/arsenic (hydro) oxides. The reductive dissolution of ferrous ion (Fe2+) occurred in the initial stage, and partly contributed to the increase of arsenic concentration in the overlying water. The increase of PO4 3− concentration in the overlying water enhanced the mobility and biological toxicity of the arsenic in the sediment. After PO4 3− in the overlying water was depleted, arsenic in the overlying water could be adsorbed and precipitated again by iron salts, resulting in the decrease of arsenic concentration in the overlying water. The study implies that among those arsenic-contaminated lakes, eutrophication will aggravate the risks of secondary pollution of arsenic.

A DFT Investigation of the Adsorption of Phosphate Ions on Co- and Ni-Doped Graphene

In this study, the adsorption of PO[Formula: see text], HPO[Formula: see text], H2PO[Formula: see text] on intrinsic, Co-doped and Ni-doped graphene has been investigated through density functional theory (DFT) calculations. Computing of final adsorption distance, adsorption energy, electron density and partial density of states shows that the adsorption between intrinsic graphene and phosphate ions is weak, and it is only physical adsorption. However, doping graphene with Ni or Co greatly enhances its adsorption with phosphate ions and leads to chemisorption. Combined with the analysis on the variation in conductance, Ni-doped graphene is more sensitive to and thus a promising material for detecting phosphate ions.

The use of pumice amended with sand media for domestic wastewater treatment in vertical flow constructed wetlands planted with lemongrass (Cymbopogon citratus)

The performance efficiency in constructed wetlands (CWs) technology is primarily affected by the media material and the types of plants used. Recently, investigations into the usage of local materials and plants in CWs has increased. Pumice is a material which is potential used as a media. However, research on amendment of pumice with other media in CWs is still limited. Therefore, this study aims to evaluate the potential of pumice amended with sand media and planted with lemongrass (Cymbopogon citratus) in CWs to remove organic matter, suspended solids, nutrients, and coliform. The adsorbents were characterized using X-ray diffraction, FTIR and XRF followed by adsorption experiments for PO4–P. Furthermore, Six vertical flow (VF) mesocosms with a diameter of 10.2cm and 55cm depth were established over six months. The treatments were based on percentage of sand media amended with pumice and planted with lemongrass. Furthermore, the barren media were applied to investigate the effect of lemongrass. The loading rate of domestic wastewater into the VF mesocosms was 2 L/day while inflows and outflows were determined for nutrients, organic matter, suspended solids and coliform. The adsorption of PO4–P followed the Langmuir model with adsorption capacity was 0.089 and 0.067 mol/g for pumice and sand, respectively. The results also showed that the removal efficiency of TSS, COD, NO3–N, NO2–N, PO4–P and total coliforms were in the range of 93.7–97.3 %, 52–83 %, 63–86 %, 51–74%, 81–88 % and 92–97 %, respectively. Based on the results, the highest removal efficiency was observed in the sand media amended with 50 % pumice and planted with lemongrass, while the lowest was found in the barren sand media.

Adsorption Properties of Waste Building Sludge for Environmental Protection

Waste building sludge (WBS) originating in the production of concrete prestressed poles (CSW) and technical stone (TSW) used in original and Fe-modified forms (CSWFe, TSWFe) was tested as an environmentally friendly and cheap sorbent of selected cations (Cd2+, Pb2+, Cs+) and anions (AsO43−, PO43−, CrO42−) from water. The experiments were performed with 0.1 and 0.5 mmol·L−1 model solutions in a batch manner at laboratory temperature. Adsorption data were fitted with the Langmuir model. The adsorption of cations (Pb2+ and Cd2+) ran almost quantitatively (>97%) on both CSW and TSW. Cesium (Cs+) adsorption on TSW reached 80%, while in the case of CSW, it was ineffective. The modification of CSW and TSW with FeII (CSWFe and TSWFe) improved their adsorption selectivity to anions by up to 70%. The adsorption of PO43− and AsO43− ran quantitatively (>98%) on modified CSWFe and TSWFe and also on initial CSW, while CrO42− was effectively adsorbed (≈80%) on TSWFe only. The adsorption affinity of tested ions in terms of adsorption capacity and sorbent consumption declined in order as follows: Pb2+ ≈ Cd2+ >> Cs+ for cations and AsO43− ≈ PO43− > CrO42− for anions.

Study on Adsorption of PO 4 3- -P in Water using Activated Clay

Study on Adsorption of PO 4 3- -P in Water using Activated Clay

Method for phosphate oxygen isotopes analysis in water based on in situ enrichment, elution, and purification

The phosphate oxygen isotope (δ18OP) ratio has been proven to be an effective tool to trace the sources and biogeochemical cycles of phosphorus (P) in aquatic ecosystems. However, the enrichment of phosphate (PO4) and the removal of impurities are quite complex and easy to cause PO4 loss in current δ18OP analytical methods. Moreover, the δ18OP value obtained by the commonly-used instantaneous sampling method is more of the instantaneous information of P, which is accidental or uncertain for accurate identification of the P source. In this study, a new method of in situ enrichment, elution, and purification of PO4 (ISEEP) was developed for δ18OP analysis in waters. This method utilized a PO4 binding phase (Zr-Oxide gel) to selectively in situ adsorb PO4 in water and exhibited an adsorption capacity per unit area of up to 789.3 μg P/cm2. The PO4 on the gel was eluted easily with a 1 M NaOH solution. More than 99.7% of the common anions, cations, and dissolved organic matter (DOM), as well as more than 90% of the trace elements were removed synchronously after adsorption and elution of PO4. The recovery rate of PO4 in the whole procedure was as high as 92.8%. The XRD and SEM examinations showed that the ISEEP can obtain high-purity Ag3PO4 solid for the δ18OP measurement. The reliability of the ISEEP method is confirmed by the measured δ18OP value and standard deviation of parallel samples from different types of natural waters obtained by both the ISEEP and the current popular McLaughlin (2004) method. It provides a good prospect of this new method for tracing the P sources and their biogeochemical cycling in aquatic ecosystems.

Competitive Adsorption of As(III), As(V), and PO4 by an Iron Oxide Impregnated Activated Carbon: Surface Complex Modeling

The objective of this study was to predict the competitive adsorption of As(III), As(V), and PO4 by an iron oxide impregnated carbon (L-Act, 9% Fe(III) amorphous iron oxide) over a range of environmental conditions using the surface complexation modeling (SCM) approach. L-Act surface complexation constants determined from a single pH-adsorption edge were used to predict pH-dependent competitive removal in singular, binary, and tertiary adsorbate systems. As(III), As(V), and PO4 complexes were modeled as bidentate binuclear species at low pH and monodentate species at high pH using the two monoprotic surface site/diffuse electric double layer model (2MDLM). F values determined based on 2MDLM predictions were close to those calculated by FITEQL (a statistical optimization program) demonstrating the effectiveness of the 2MDLM in describing adsorption behavior. F values were generally in the recommended range of 0.1–20 indicating a good fit between the data and the model. The 2MDLM also successfully predicted As(III)/As(V)/PO4 adsorption data of hydrous ferric oxide and goethite adsorbents from the literature.

Biomass pyrolysis with alkaline-earth-metal additive for co-production of bio-oil and biochar-based soil amendment

The alkaline-earth-metal (AEM) has a good performance on modification of both bio-oil and biochar during biomass pyrolysis. In this work, the pyrolysis of rice husk (RH) in the presence of CaO, CaCO3, MgO and MgCO3 was comparatively studied for selecting an appropriate AEM additive to balance the qualities of pyrolytic products. Pyrolysis of RH with the AEM additives could decrease the acids content and increase the hydrocarbons content in bio-oil. Compared with the Ca-additives (i.e., CaO, CaCO3), the Mg-additives (i.e., MgO, MgCO3) were more beneficial for enhancing the hydrocarbons production. The addition of biochar to soil can significantly enhance the water retention. RHC-MgCO3 had a maximum water retention capacity, while RHC-MgO had a minimum water retention capacity due to its lowest specific surface area. Additionally, the Mg-modified biochar had a much higher nutrient (i.e., K+, PO43−) adsorption capacity. In particular, RHC-MgO with a lowest specific surface area had a highest PO43− adsorption capacity, which was evidenced by the adsorption of PO43− onto biochar mainly controlled by the chemisorption process. PO43− adsorbed in the RHC-MgO released rapidly indicating its low PO43− retention capacity. In general, MgCO3 would be an appropriate candidate that is used in pyrolysis of biomass for co-production of bio-oil and biochar composite with high capacities of water/nutrient adsorption and retention for soil amendment.

Ternary Complex Formation of Phosphate with Ca and Mg Ions Binding to Ferrihydrite: Experiments and Mechanisms

Calcium (Ca) and magnesium (Mg) are the most abundant alkaline-earth metal ions in nature, and their interaction with ferrihydrite (Fh) affects the geochemical cycling of relevant ions, including phosphate (PO4). The interfacial interactions of Ca and Mg (M2+) with PO4 have not been analyzed yet for freshly precipitated Fh. Here, we studied experimentally this interaction in binary M2+-PO4 systems over a wide range of pH, M2+/PO4 ratios, and ion loadings. The primary adsorption data were scaled to the surface area of Fh using a recent ion-probing methodology that accounts for the size-dependent chemical composition of this nanomaterial (FeO1.4(OH)0.2·nH2O). The results have been interpreted with the charge distribution (CD) model, combined with a state-of-the-art structural surface model for Fh. The CD coefficients have been derived independently using MO/DFT/B3LYP/6-31+G** optimized geometries. M2+ and PO4 mutually enhance their adsorption to Fh. This synergy results from the combined effect of ternary surface complex formation and increased electrostatic interactions. The type of ternary complex formed (anion- vs cation-bridged) depends on the relative binding affinities of the co-adsorbing ions. For our Ca-PO4 systems, modeling suggests the formation of two anion-bridged ternary complexes, i.e., ≡(FeO)2PO2Ca and ≡FeOPO3Ca. The latter is most prominently present, leading to a relative increase in the fraction of monodentate PO4 complexes. In Mg-PO4 systems, only the formation of the ternary ≡FeOPO3Mg complex has been resolved. In the absence of Ca, the pH dependency of PO4 adsorption is stronger for Fh than for goethite, but this difference is largely, although not entirely, compensated in the presence of Ca. This study enables the use of Fh as a proxy for the natural oxide fraction, which will contribute to improved understanding of the mutual interactions of PO4 and M2+ in natural systems.

PO4 adsorption on the calcite surface modulates calcite formation and crystal size

Abstract Calcium carbonate (CaCO3) and particularly its stable phase, calcite, is of great geological significance in the deep carbon cycle since CaCO3 from biomineralized shells and corals form sedimentary rocks. Calcite also attracts attention in medical science and pharmacy as a primary or intermediate component in biomaterials because it possesses excellent biocompatibility along with suitable physicochemical properties. Calcite blocks have already been used during surgical procedures as a bone substitute for reconstructing bone defects formed by diseases and injury. When producing CaCO3 biomaterials and bioceramics, in particular, in vivo control of the size and polymorphic nature of CaCO3 is required. In this study, we investigated the effects of PO4 on calcite formation during the phase conversion of calcium sulfate anhydrate (CaSO4, CSA), which is sometimes used as a starting material for bone substitutes because of its suitable setting ability. CSA powder was immersed in 2 mol/L Na2CO3 solution containing a range of PO4 concentrations (0–60 mmol/L) at 40 °C for 3 days. The treated samples were investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray fluorescence spectroscopy, and thermal analysis. In addition, the fine structures of the treated samples were observed by field-emission scanning electron microscopy, and the specific surface area was measured. We found that PO4, which is universally present in vivo, can modulate the calcite crystal size during calcite formation. A fluorescence study and calcite crystal growth experiments indicated that PO4 adsorbs tightly onto the surface of calcite, inhibiting crystal growth. In the presence of high PO4 concentrations, vaterite is formed along with calcite, and the appearance and stability of the CaCO3 polymorphs can be controlled by adjusting the PO4 concentration. These findings have implications for medical science and pharmacology, along with mineralogy and geochemistry.

PO43− adsorption in a complex solution by nickel–cobalt hydroxide, and its cytotoxicity on bovine aortic endothelial cells

A nickel–cobalt complex hydroxide was prepared by mixing nickel and cobalt in the ratio of 9:1 (NC91-virgin) and then performing calcination at 280 °C (NC91-280). The adsorption of PO43− by both NC91-virgin and NC91-280 in a complex solution system was evaluated. A higher amount of PO43− was adsorbed by NC91-280 than by NC91-virgin. These results suggest that the adsorption of PO43− is related to the physicochemical properties of the adsorbents. In addition, PO43− was selectively adsorbed by NC91-280 in the complex solution. A pH of approximately 2–3 was optimal for the adsorption of PO43−. The amount of adsorbed PO43− increased with temperature. The adsorption isotherm data were applied to both the Freundlich and Langmuir models. NC91-280 was reused for the adsorption/desorption of PO43− at five times. We could confirm a high recovery percentage of PO43− using a NaOH solution at 1000 mmol/L under the tested experimental conditions. Moreover, we could elucidate the mechanism behind PO43− adsorption in the complex solution. The intensity of P on the surface of NC91-280 increased after adsorption, and peaks of P(2s) and P(2p) were detected by X-ray photoelectron spectroscopy. Finally, we showed that NC91-280 had low a cytotoxic effect on vascular endothelial cells.

Adsorption mechanisms of chromate and phosphate on hydrotalcite: A combination of macroscopic and spectroscopic studies

Hydrotalcite (HT) is a layered double hydroxide (LDH), which is considered as a potential adsorbent to remove anion contaminants. In this study, adsorption of chromate (CrO4) and phosphate (PO4) on HT was conducted at various pH and temperatures. Related adsorption mechanisms were determined via the isotherm, kinetic, and competitive adsorption studies as well as the Cr K-edge X-ray absorption fine-structure (XAFS) spectroscopy. The maximum adsorption capacities for CrO4 and PO4 on HT were 0.16 and 0.23 mmol g−1. Regarding adsorption kinetics, CrO4 and PO4 adsorption on HT could be well described by the second order model, and the rate coefficient of CrO4 and PO4 on HT decreased significantly with the increasing pH from 5 to 9. The adsorption kinetics for CrO4 and PO4 were divided into fast and slow stages with the boundary at 15 min. This biphasic adsorption behavior might be partially attributed to multiple reactive pathways including anion exchange and surface complexation. Fitting results of Cr K-edge EXAFS analysis showed a direct bonding between CrO4 and Al on HT surfaces. Such a surface complexation appeared to be the rate-limiting step for CrO4 adsorption on HT. By contrast, the diffusion through the hydrated interlayer space of HT was the major rate-limiting step for PO4. This study determined the adsorption behaviors of CrO4 and PO4 on HT, including the initial transfer process and the subsequent adsorption mechanisms. Such information could improve the strategy to use HT as the potential adsorbent for the remediation of anionic pollutants.

Microstructure and rheology of bentonite slurries containing multiple-charge phosphate-based additives

The multiple-charge phosphate-based additives affected the rheology of bentonite gels differently. The yield stress decreased with increasing concentration of additives. However for the triple-charge additives, PO43− and cyclic P3O93− the maximum extent of yield stress reduction was only about 50%. For the higher multiple-charge additives, P2O74−, P3O105− and (PO3−)17 the decrease was >95% where yield stress of <1 Pa was attained at high concentration. The cryo-SEM images of the bentonite gels under the influence of various phosphate additives showed similar microstructure as the untreated gels. An exception was that treated with 10 dwb% (NaPO3)17 where the microstructure showed evidence of structural collapse with more lying platelets facing up. A positive site per anion adsorption model for PO43− and the close proximity of charge sites was invoked to explain its poor performance in yield stress and viscosity reduction. The adsorption of PO43− on adjacent sites is not possible because of charge repulsion between the anions due their close proximity to explain the low adsorption. The number of positive sites per anion adsorption was larger for the higher multiple-charge additives such as 2 for P2O74− and 3 for P3O105− and a few more for the (PO3−)17 was responsible for their higher adsorption and this was responsible for the identical decreasing yield stress trend with additive concentration observed. The 6-member ring anion, P3O93−, adsorption is poor due to its low charge and bulky structure.

Carbonate Adsorption to Ferrihydrite: Competitive Interaction with Phosphate for Use in Soil Systems.

Carbonate (CO3) interacts with Fe-(hydr)oxide nanoparticles, affecting the availability and geochemical cycle of other important oxyanions in nature. Here, we studied the carbonate–phosphate interaction in closed systems with freshly prepared ferrihydrite (Fh), using batch experiments that cover a wide range of pH values, ionic strength, and CO3 and PO4 concentrations. The surface speciation of CO3 has been assessed by interpreting the ion competition with the Charge Distribution (CD) model, using CD coefficients derived from MO/DTF optimized geometries. Adsorption of CO3 occurs predominately via formation of bidentate inner-sphere complexes, either (≡FeO)2CO or (≡FeO)2CO··Na+. The latter complex is electrostatically promoted at high pH and in the presence of adsorbed PO4. Additionally, a minor complex is present at high CO3 loadings. The CD model, solely parametrized by measuring the pH-dependent PO4 adsorption as a function of the CO3 concentration, successfully predicts the CO3 adsorption to Fh in single-ion systems. The adsorption affinity of CO3 to Fh is higher than to goethite, particularly at high pH and CO3 loadings due to the enhanced formation (≡FeO)2CO··Na+. The PO4 adsorption isotherm in 0.5 M NaHCO3 can be well described, being relevant for assessing the reactive surface area of the natural oxide fraction with soil extractions and CD modeling. Additionally, we have evaluated the enhanced Fh solubility due to Fe(III)-CO3 complex formation and resolved a new species (Fe(CO3)2(OH)23−(aq)), which is dominant in closed systems at high pH. The measured solubility of our Fh agrees with the size-dependent solubility predicted using the surface Gibbs free energy of Fh.

Role of phosphate in ruthenium-complex-sensitized TiO2 system for hydrogen production: Mechanism and kinetics

Most Ru(II) complex-sensitized TiO2 systems for hydrogen (H2) production suffer from instability of the photosensitized system because the anchoring groups of Ru(II) dyes, which are required for their adsorption on TiO2, are intrinsically vulnerable to chemical and photochemical cleavage. In this study, a new method that enables the use of a Ru(II) dye without any anchoring groups (Ru(bpy)32+) was developed and investigated. The stable photocatalytic efficiency in repeated H2 production cycles under visible-light irradiation indicates that the Ru(II) dye without anchoring groups is highly stable during dye-sensitized H2 production. The dye-sensitized H2 production in the Ru(bpy)32+-sensitized TiO2 system comprising Ru(bpy)32+ as a photosensitizer, platinized TiO2 (Pt-TiO2) as a cocatalyst-electron mediator, and ethylenediaminetetraacetic acid as an electron donor was negligible. However, the addition of phosphate (PO43–) to the Ru(bpy)32+-sensitized TiO2 system enabled the production of H2 via dye sensitization in the absence of any anchoring groups on the dye. The adsorption of PO43– changed the surface charge of Pt-TiO2 from positive to negative under acidic conditions, thereby inducing adsorption of cationic Ru(bpy)32+ on the surface of Pt-TiO2 and facilitating electron transfer from excited Ru(bpy)32+ to the conduction band of TiO2. The PO43– adsorption-induced change in the surface charge and the subsequent adsorption of Ru(bpy)32+ on the surface of PO43–-adsorbed Pt-TiO2 were confirmed by zeta potential measurements and Fourier transform infrared spectroscopy, respectively. In contrast with H2 production, the presence of PO43– had little effect on the kinetics of anionic chromate (CrO42–) reduction in the Ru(bpy)32+-sensitized TiO2 system. This result indicates that electron transfer from Pt to the electron acceptor on PO43–-adsorbed Pt-TiO2 is highly dependent on the charge character of the electron acceptor (i.e., electron transfer to the cationic electron acceptor is more favored). The negative charge on the surface of Pt-TiO2 induced by the adsorption of PO43– attracts the positively charged protons to the surface, which kinetically enhanced electron transfer from Pt to the protons. The (photo)electrochemical data demonstrate that PO43– adsorbed on Pt-TiO2 facilitates the interfacial electron transfer processes by enhancing the adsorption of Ru(bpy)32+ and attracting protons to the surface. The positive effect of PO43– on H2 production increased with increasing PO43– concentration and decreasing pH, where the conditions are more favorable for PO43– and proton adsorption on the surface of Pt-TiO2. Among the five anions evaluated in this study (PO43–, AsO43–, F–, NO3–, and SO42–), PO43– was most efficient and facilitated stable H2 production.

Adsorption performance and mechanism for phosphate removal by cerium hydroxide loaded on molecular sieve

Abstract Cerium hydroxide loaded on molecular sieve (CHMS) was investigated for phosphate (PO4) adsorption. As the initial phosphorus concentration was set as 5 mg L−1, CHMS possessed high PO4 adsorption capacity at 25 °C compared with COMS (ceria loaded on molecular sieve) and MS (molecular sieve), and can be extensively applied in wide pH range (4–11). Based on kinetics and isotherms analysis, the adsorption process was mainly chemisorption and multilayer adsorption procedure. In addition, most of the coexisting ions had little effect on PO4 adsorption, in spite of 2 orders of magnitude higher levels than PO4. CHMS showed the excellent regeneration (at least 5 times recycling) ability with 1 M NaOH. The proposed mechanisms were explicated by various analytical techniques XRD, TG, XPS, and NMR analysis and found that Ce(HPO4)2 and Ce3(PO4)4 were the main pathways after adsorption, and the activated site of adsorbent was dependent on the presence of cerium hydroxide. Consequently, CHMS was a promising adsorbent for PO4 removal from wastewater.

Phosphate Removal in Relation to Structural Development of Humic Acid-Iron Coprecipitates

Precipitation of Fe-hydroxide (FH) critically influences the sequestration of PO4 and organic matter (OM). While coatings of pre-sorbed OM block FH surfaces and decrease the PO4 adsorption capacity, little is known about how OM/Fe coprecipitation influences the PO4 adsorption. We aimed to determine the PO4 adsorption behaviors on humic acid (HA)-Fe coprecipitates in relation to surface and structural characteristics as affected by HA types and C/(C + Fe) ratios using the Fe and P X-ray absorption spectroscopy. With increasing C/(C + Fe) ratios, the indiscernible changes in the proportion of near-surface C for coprecipitates containing HA enriched in polar functional groups implied a relatively homogeneous distribution between C and Fe domains. Wherein PO4 adsorbed on FH dominated the P inventory on coprecipitates, yielding PO4 sorption properties nearly equivalent to that of pure FH. Structural disruptions of FH caused by highly associations with polar functional groups of HA enhanced the C solubilisation. While polar functional groups were limited, coprecipitates consisted of core FH with surface outgrowth of HA. Although surface-attached HA that was vulnerable to solubilisation provided alternatively sites for PO4 via ternary complex formation with Fe bridges, it also blocked FH surfaces, leading to a decrease in PO4 adsorption.