Formation Of Surface Complexes Research Articles

Caesium-Iodide-Assisted Synthesis of High-Quality, Stable, and Robust Lead-Free Perovskite Quantum Dots.

The poor morphology, and susceptibility to oxidation of tin-based perovskite quantum dots (TQDs) have posed significant challenges, limiting their application potential. This study presents a straightforward method for synthesizing high-quality CsSnI3-based perovskite quantum dots (TQDs) by incorporating a mixed Cs source of Cs2CO3 and CsI. The addition of CsI increased the I:Sn ratio while maintaining Sn:Cs, resulting in TQDs with smaller size and improved uniformity. X-ray photoelectron spectroscopy (XPS), and Nuclear magnetic resonance (NMR) analyses confirmed enhanced crystallinity, photoluminescence intensity, and antioxidation ability of CsI-TQDs. Remarkably, these TQDs exhibit exceptional stability, enduring over 1 h in air and more than 24 h before complete oxidation, surpassing the previously reported longest lifetime in air for TQDs with conventional oleic acid (OA) and oleylamine (OAm) ligands. Furthermore, these TQD films retain robustness after ligand exchange with methyl acetate (MeOAc) and formamidinium iodide (FAI), representing the first successful short-ligand exchange of TQDs and enabling further electronic device applications. These findings suggest that CsI in the Cs source plays a crucial role in facilitating the formation of surface complexes, regulating TQD growth and suppressing iodine vacancies.

Efficient activation of peroxyacetic acid by cobalt-iron alloy/oxide heterojunctions anchored in defect-rich biochar for pesticide degradation in water: Unravelling the radical-unradical mechanism

The activation processes of peracetic acid (PAA-AOPs) have garnered significant attention in wastewater treatment. In this study, an amorphous carbon-modified bimetallic CoFe alloy/oxide catalyst (CoFe@DBCx-y, where x represents biomass mass and y represents pyrolysis temperature) was developed to activate PAA for the degradation of organochlorine pesticides (OCPs). Due to the size effect, biochar dynamically regulates the particle size of metal species, which is influenced by the pyrolysis temperature. Among these systems, the CoFeDBC2.0–700/PAA oxidation system effectively removed 95.7 % of 2,4-dichlorophenoxyacetic acid (2,4-D), exhibiting a kinetic constant 1.7 times higher than that of the Nano/PAA system. Furthermore, quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that high-valent metal oxides (MIV = O) and singlet oxygen (1O2) are the primary active species responsible for the removal of 2,4-D, whereas organic radicals (RO·) and hydroxyl radicals (·OH) play a secondary role. Electrochemical and Raman spectroscopy tests revealed the formation of a metastable surface complex (≡Co(III)–OO(O)CCH3) between PAA and the catalyst, which acted as an intermediate oxidant to generate reactive oxygen species (ROS) through a chain reaction. Carbon defects in the biochar functioned as an electron source, continuously replenishing the electrons consumed in the reaction and facilitating the valence cycling between Co and Fe. This study provides new insights into the remediation of pesticide-contaminated wastewater using PAA-AOPs with heterogeneous bimetallic carbon-based catalysts.

Synthesis, characterization and study of Sb(Ⅲ) adsorption from aqueous solution by iron-aluminum pillared attapulgite

In this study, a simple, environmentally friendly and inexpensive adsorbent for Sb(III) in aqueous solution was prepared by the copolymerization method using attapulgite as the matrix, FeCl3 and AlCl3 as the metal sources. The morphology and structure of iron-aluminum pillared attapulgite were analyzed through various characterization methods. The conditions and influencing factors of iron-aluminum pillared attapulgite preparation and Sb(III) adsorption were studied. The saturated adsorption capacity of Sb(III) could reach 60.44 mg·g−1 for 180 min at pH 7 and 298 K. The adsorption process is conformed to Langmuir isothermal model and pseudo-second-order kinetic model, and the thermodynamic investigation suggested a spontaneous and endothermic adsorption process. It was revealed by X-ray photoelectron spectroscopy analysis and Zeta potential analysis that Sb(III) was first electrostatically adsorbed by the adsorbent, part of Sb(III) was oxidized to Sb(V) by Fe(III) and then antimony was complexed with iron and aluminum hydroxides to form surface complexes. In addition, a small amount of antimony migrated through intra-particle diffusion into the internal micropores and reacted with hydroxyl groups. Most coexisting components under the chosen conditions had no influence on Sb(III) adsorption, and PO43−, AsO33−, C6H8O7 and H2C2O4 had a negligible effect. However, the adsorption capacity of over 90 % without interference showed that the material has a strong selectivity for Sb(III) adsorption. The findings of the desorption experiment showed that the adsorption product has a considerable degree of desorption at increased hydrochloric acid concentrations. It may be concluded that the adsorption product is more stable in the overall polluted water environment since the actual acidity of the polluted water environment is significantly lower than the desorption experiment acidity. Overall, iron-aluminum pillared attapulgite has great potential for application in removing Sb(III).

Uranium removal from contaminated groundwater using goethite-loaded composite microporous membrane

In this study, we have coupled adsorption and membrane separation for the removal of uranium from contaminated groundwater in environmentally relevant conditions at low energy requirements. This study mainly focuses on elucidating uranium, U(VI), adsorption mechanisms using surface complexation modeling approach in a novel goethite-loaded composite microfiltration membrane (GLM). This experiment involved immobilizing goethite nanorods in a microporous (0.22 μm pore size) poly (vinylidene fluoride) (PVDF) membrane. The effect of varying goethite loading and hydraulic residence time on U(VI) removal was investigated at field-relevant pH (i.e. pH 8.5). U(VI) adsorption (i.e. 4.95 μg·mg−1) was optimum at a goethite loading 1.20 mg·cm−2. The effect of varying hydraulic residence time had no impact on U(VI) removal which was also confirmed via performing batch adsorption kinetic experiments. GLM membrane loaded at 1.2 mg·cm−2 could treat 275 L of U(VI) contaminated water having 200 μg of U L−1 below WHO drinking water limit (i.e. 30 μg of U L−1) with 1 m2 of membrane surface area with a adsorption capacity of 6.12 μg·mg−1. Varying the pH of aqueous solution, containing U(VI) from pH 4.0 to pH 10.0, showed a significant impact on uranium uptake ranging from 0.7 μg·mg−1 to 2.63 μg·mg−1 by the composite membrane. The adsorption mechanism of uranium onto goethite was explained via the formation of bidentate surface complexes using the Surface Complexation Model (SCM). The results of batch pH edge experiments and SCM have been compared with pH experiments performed using GLM. The results of SCM predicted the batch pH edge experiment within a RMSE of 0.055. The trend of U(VI) removal in membrane experiments was observed to be similar to that of batch pH edge experiments and was well predicted SCM model. Our results showed that the novel goethite-loaded membrane has the potential for the effective removal of uranium with a lower specific energy consumption.

The Effects of Montmorillonite–Humic Acid Composite Particles on the Photolysis of Tetracycline in Water

Suspended particulate matter (SPM) is an important component of natural water bodies and can significantly influence the photolytic behavior of water pollutants. A comprehensive understanding of the photochemical behavior of water pollutants in natural waters requires consideration of the presence of SPM. In this study, montmorillonite–humic acid (MMT-HA) composite particles were synthesized to simulate SPM in natural waters and their effects on the photolysis of tetracycline (TC) were investigated. The results demonstrated that the presence of MMT-HA composite particles in water significantly enhanced the photolysis of TC, with the photolytic kinetics following a pseudo-first-order model. Electron spin resonance spectra and free radical quenching experiments indicated that the photoactive components (MMT and humic acids) in the composite particles induced the generation of reactive oxygen species under light exposure, further contributing to the enhanced photolysis of TC. Comparative analysis of the free radical signals and adsorption experiments revealed that the accelerated photolysis of TC was also related to the interfacial interaction between the MMT in the composite particles and the TC molecules. The formation of surface complexes between TC molecules and the negatively charged sites on the MMT surface facilitated light absorption and electron transfer, thereby accelerating the photolysis of TC. Photoproduct analysis indicated that the primary degradation pathways of TC in the composite particle systems included the addition of hydroxyl radicals to the aromatic ring, as well as demethylation, deamination and dehydration in the side chains. This study shows that SPM in water bodies can affect the photochemical behavior of pollutants and should be taken into account when assessing the phototransformation of pollutants in natural waters.

The fate of cadmium during ferrihydrite phase transformation affected by dissolved organic matter: Insights from organic-mineral interaction

Ferrihydrite (Fh) is an important scavenger for sequestering cadmium (Cd). However, Fh is poorly crystallized and tends to undergo phase transformation under the impact of dissolved organic matter (DOM). The roles of DOM in Fh transformation pathway and the consequent Cd2+ remobilization behavior remain debate due to its structural heterogeneity and diversity. Herein, formic acid (FA), oxalic acid (Ox), and citric acid (CA) were selected as model DOM, which have one, two, and three carboxyl ligands, respectively. Fe K-edge extended X-ray absorption fine structure (EXAFS) spectra revealed an organic-specific correlation between Fh transformation and Cd2+ transport. FA with monodentate carboxyl ligand, lacking binding with Fh particles, had negligible influence on transformation dynamics and Cd2+ transport. The complexation of bidentate Ox with Fh particles impaired the stability of Fe(O,OH)6 octahedra, accelerating Fh phase transformation, thereby increasing Cd2+ release. During the subsequent recrystallization, Ox guided crystal growth via oriented attachment, which possibly occluded the remaining Cd2+ within structural defects of the secondary minerals. Conversely, tridentate CA exhibited a strong affinity with Fh, resulting in the formation of ferric citrate surface complexes that stabilized Fh against transformation and thus enhanced the long-term immobilization of Cd2+. These findings highlight the significant role of organic-ion/mineral interactions in Fh transformation, which are fundamentally linked to predicting Cd2+ transport behavior in environmental systems.

Gluconate and formate uptake by hydrated cement phases

The uptake of formate and gluconate by C–S–H, AFm phases, ettringite and hydrated Portland cement (PC) was studied at pH 13 by batch sorption experiments. The formation of gluconate and formate-AFm phases was observed in pure systems, but not in hydrated cement. Gluconate sorbs more strongly on AFm phases and ettringite than formate. Higher calcium concentrations increase the gluconate sorption on C–S–H and hydrated Portland cements due the formation of Ca-gluconate surface complexes on C–S–H. Measured Rd values for gluconate sorption on C–S–H increase from 2.0 dm3‧kg−1 for C–S–H with Ca/Si = 0.8 to 34 dm3‧kg−1 for Ca/Si = 1.4 at pH 13. They are a factor 5 to 10 higher at lower pH values, and higher Ca-concentrations. Calcium concentration does not significantly affect the uptake of formate by C–S–H. Formate sorbs on hydrated PC with Rd values in the range of 3–33 dm3‧kg−1.

Enhanced adsorption of Cr(VI) from aqueous solutions by CTAB-modified schwertmannite: Adsorption performance and mechanism

Schwertmannite (Sch) is recognized for its heavy metal adsorption capabilities, but is limited by several drawbacks, including a narrow pH operational range, a tendency towards agglomeration, and a relatively modest adsorption capacity, which restricts its widespread utilization. This study introduces cetyltrimethylammonium bromide (CTAB) modified Sch (CTAB-Sch), synthesized through a rapid oxidation technique using H2O2, which significantly ameliorates these limitations. The investigation finds that a CTAB concentration of 10 mM is optimal for Cr(VI) removal, with the modified sch showing significant improvements in stability, recyclability, and adsorption efficiency within a pH range of 2–7. The adsorption process is characterized as spontaneous and endothermic, conforming to pseudo-second-order kinetics and the Langmuir adsorption model, resulting in a maximum adsorption capacity of 103.02 mg/g, which is approximately twice that of its unmodified Sch. Through comprehensive experimental analysis, the efficient removal mechanism of Cr(VI) by CTAB-Sch was elucidated, involving ion exchange, electrostatic attraction, and surface complex formation. Moreover, the investigation demonstrates that CTAB plays a pivotal role in enhancing adsorption by optimizing functional group orientation, amplifying surface positive charge, augmenting hydrophilicity, and inhibiting mineral agglomeration. The findings suggest that CTAB-Sch has significant potential for treating Cr(VI)-contaminated wastewater, highlighting its advancements in adsorption technology.

Mechanism of efficient adsorption for arsenic in aqueous solution by zeolitic imidazolate framework‑8.

Arsenic (As) is one extremely hazardous and carcinogenic metalloid element. Due to mining, metal smelting, and other human activities, the pollution of water (especially groundwater) and soil caused by As is increasingly serious, which badly threatens the environment and human health. In this study, a zeolite imidazolate framework (ZIF-8) was synthesized at room temperature and employed as an adsorbent to facilitate the adsorption of As(III) and As(V) from the solution. The successful synthesis of ZIF-8 was demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) revealed that its particle size was approximately 80nm. The adsorption kinetics, adsorption isotherm, solution pH, dose, coexisting ions, and the synonymous elements antimony (Sb) were conducted to study the adsorption of As by ZIF-8 nanoparticles. The maximum saturation adsorption capacity was determined to be 101.47mg/g and 81.40mg/g for As(III), and As(V) at initial pH = 7.0, respectively. Apparently, ZIF-8 had a good removal effect on As, and it still maintained a good performance after four cycles. The coexisting ions PO43- and CO32- inhibited the adsorption of both As(III) and As(V). ZIF-8 performed well in removing both As and Sb simultaneously, although the presence of Sb hindered the adsorption of both As(III) and As(V). Both FTIR and XPS indicated the adsorption mechanism of As on ZIF-8: ZIF-8 generates a large amount of Zn-OH on the surface through hydrolysis and partial fracture of Zn-N, both of which form surface complexes with As.

Understanding arsenic-ulexite interactions in evaporite environments: Evidence from XRPD, micro-XRF, micro-FT-IR, and XPS studies

World-class borate deposits often form from As-rich waters, this study addresses the understudied association of arsenic (As) species with evaporite borates, focusing on the Puna region's borate deposits (Central Andes of Argentina). The research aims to characterize the association between borate minerals and high As concentrations in brines and thermal waters. To achieve this, five borate samples were collected from the Olaroz salt flat nucleus and thermal springs, alongside associated water samples. Comprehensive analytical techniques, including ICP-MS, ICP-OES, synchrotron-based micro-XRF, XRPD, Rietveld analysis, micro-FT-IR, and XPS, were employed to determine bulk and surface chemical compositions, mineral identification, and solid speciation of As and boron. The study reveals that under oxidizing conditions and in absence of organic matter, aqueous arsenic species interact with ulexite through a stepwise process involving charge neutralization, cationic bridge formation, and surface complex formation with polyborate and As(V) oxyanions. However, in environments associated with microbial mats or organic-rich sediments, the dissolved As(V) is reduced to As(III), which forms complexes with functional groups of organic matter. The coexistence of As(III) and As(V) in specific layers suggests potential remediation strategies targeting organic matter for the removal of the more toxic As(III) in similar geological settings.

Sorption of U(VI) on MX-80 Bentonite and Granite in Ca-Na-Cl Saline Solutions

Uranium has been identified as an element of interest for the safety assessment of a deep geological repository for used nuclear fuel. This paper examines the sorption behavior of U(VI) onto MX-80 bentonite and granite in Ca-Na-Cl solutions of varying ionic strengths [0.05 to 3 mol/kgw (m)] and across a pH range of 4 to 10. U(VI) sorption on MX-80 showed that U(VI) sorption gradually increased with pHm until pHm = 6, where it reached its maximum, and decreased slightly with pHm until pHm = 8, and then became constant. U(VI) sorption on granite increased along with pHm, reached the maximum around pHm = 7 to 8, and then slightly decreased with pHm. Both MX-80 and granite showed essentially no ionic strength dependence for sorption of U(VI). A nonelectrostatic surface complexation model successfully predicted sorption of U(VI) onto MX-80 and granite using the formation of an inner-sphere surface complex. Optimized values of surface complexation reaction constants (log K0) for the formation reactions of these surface species are proposed.

Analyzing (3-Aminopropyl)triethoxysilane-Functionalized Porous Silica for Aqueous Uranium Removal: A Study on the Adsorption Behavior.

This study synthesized (3-aminopropyl)triethoxysilane-functionalized porous silica (AP@MPS) to adsorb aqueous uranium (U(VI)). To comprehensively analyze the surface properties of the AP@MPS materials, a combination of SEM, BET, XPS, NMR, and zeta potential tests were conducted. The adsorption experiments for U(VI) revealed the rapid and efficient adsorption capacity of AP@MPS, with the solution condition of a constant solution pH = 6.5, an initial U(VI) concentration of 600 mg × L-1, a maximum U(VI) capacity of AP@MPS reaching 381.44 mg-U per gram of adsorbent, and a removal rate = 63.6%. Among the four types of AP@MPS with different average pore sizes tested, the one with an average pore size of 2.7 nm exhibited the highest U(VI) capacity, particularly at a pH of 6.5. The adsorption data exhibited a strong fit with the Langmuir model, and the calculated adsorption energy aligned closely with the findings from the Potential of Mean Force (PMF) analysis. The outcomes obtained using the Surface Complex Formation Model (SCFM) highlight the dominance of the coulombic force ΔG0coul as the principal component of the adsorption energy (ΔG0ads). This work garnered insights into the adsorption mechanism by meticulously examining the ΔG0ads across a pH ranging from 4 to 8. In essence, this study's findings furnish crucial insights for the future design of analogous adsorbents, thereby advancing the realm of uranium(VI) removal methodologies.

Batch adsorption study of Congo Red dye using unmodified Azadirachta indica leaves: isotherms and kinetics

Abstract A low-cost adsorbent developed from unmodified Azadirachta indica leaves was used for adsorptive removal of the Congo Red dye from an aqueous medium. The adsorbent was characterized by the Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) techniques. For optimization of operational parameters such as dye concentration, solution pH, adsorbent dose, contact time, and temperature, batch adsorption experiments were performed. It was found that for neem leaves powder (NLP), the optimum conditions were as follows: adsorbent dose of 0.8 g, contact time of 100 min having a solution with pH value of 5, adsorbate initial concentration of 40 ppm at temperature 60 °C where maximum amount of dye, i.e., 84%, removal was observed. The process followed pseudo-first-order kinetics, which reveals physical adsorption. According to isothermal investigations, sorption data were best fit with the Freundlich isotherm model. Thermodynamically, the adsorption of the Congo Red dye by the neem leaf powder was exothermic. Furthermore, the mechanistic removal of the Congo Red dye by the NLP has been explored with the help of the surface complex formation (PHREEQC) mechanism. Overall, the results of the study explore the promising nature of NLP for Congo Red dye removal.

Nitrogen-doped carbon enhances Fe0 activation for efficient tetrabromobisphenol a decontamination and its removal mechanism

Biomass derived N-doped carbon-encapsulated nano zero-valent iron (NC@Fe0) was successfully used to activate hydrogen peroxide (H2O2) for efficient oxidation of tetrabromobisphenol A (TBBPA). The as-prepared NC@Fe0 exhibited high H2O2 activation performance, with a TBBPA removal efficiency of 95.9 % and an oxidation rate constant of 0.031 min−1. The quenching experiments and electrochemical tests showed that the overall contributions of nonradical pathways were over 83.0 %, via synergistic production of singlet oxygen (1O2) and an electron transfer process (ETP). Specifically, the N group on NC@Fe0 greatly enhanced 1O2 production, while formation of surface complexes (OVs-H2O2) was responsible for the ETP mechanism. High Performance Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometer (HPLC-Q-TOF MS/MS) and Toxicity Estimation Software Tool (T.E.S.T) clearly demonstrated that products were mainly generated via debromination and β-scission, where the products were less toxic than the parent. During practical wastewater, in both lake water and domestic wastewaters, NC@Fe0/H2O2 removed over 91.0 % of TBBPA. This study highlighted the considerable contribution of nonradicals in contaminant removal and enriched our understandings of a green activator for future environmental remediations.

Development of granular composites based on laponite and Zr/Fe-alginate for effective removal of uranium (VI) from sulfate solutions

The object of research is granular composites based on zirconium-iron alginates and laponite. The task of research is to determine the influence of the Zr:Fe ratio on the structure of granular composites and efficiency of uranium (VI) removal from aqueous solutions. The influence of the zirconium and iron ratio on the parameters of the material's pore structure has been established, particularly on the change in the content of micropores within the matrix. The specific surface area of the materials ranges from 86 to 112 m²/g. The sorption properties of the composites regarding uranium (VI) have been investigated. The impact of the charge of surface groups and the form of uranium (VI) presence in sulfate solutions on their sorption characteristics has been demonstrated. The maximum adsorption capacity reaches 265.1 µmol/g at pH 6. It is shown that an elevated electrolyte content positively affects the efficiency of uranium (VI) removal in neutral and alkaline medium. It has been established that structural changes in the materials occur due to the intensive interaction of iron ions and alginate molecules, resulting in the formation of a dense gel-like structure. The mechanism of uranium (VI) removal is associated with the formation of surface complexes in the presence of electrolytes. The synthesized granulated composites exhibit improved removal efficiency of uranium (VI) under conditions of high mineralization of solutions, making them attractive for potential use as sorbents. The obtained results can be utilized in the development of effective methods for purifying water environments from uranium (VI) in high mineralization conditions, which is a relevant issue in the field of nuclear energy and the removal of radioactive substances from water systems

Comparative Screening Study on the Adsorption of Aqueous Pb(II) Using Different Metabolically Inhibited Bacterial Cultures from Industry

The global concern about the water pollution caused by heavy metals necessitates effective water treatment methods. Adsorption, with its substantial advantages, stands out as a promising approach. This study delves into the efficiency of Pb(II) removal using metabolically inhibited microbial cultures. These cultures encompass waste-activated sewage sludge (SS), industrially sourced bioremediation microbes (commercial 1—C1 and commercial 2—C2), an industrially acquired Pb(II) remediating consortium (Cons), and refined strains (derived from Cons) of Paraclostridium bifermentans (PB) and Klebsiella pneumoniae (KP). Our findings reveal maximum Pb(II) adsorption capacities of 141.2 mg/g (SS), 208.5 mg/g (C1), 193.8 mg/g (C2), 220.4 mg/g (Cons), 153.2 mg/g (PB), and 217.7 mg/g (KP). The adsorption kinetics adhere to a two-phase pseudo-first-order model, indicative of distinct fast and slow adsorption rates. Equilibrium isotherms align well with the two-surface Langmuir model, implying varied adsorption sites with differing energies. The Crank mass transfer model highlights external mass transfer as the primary mechanism for Pb(II) removal. Surface interactions between sulfur (S) and lead (Pb) point to the formation of robust surface complexes. FTIR analysis detects diverse functional groups on the adsorbents’ surfaces, while BET analyses reveal non-porous agglomerates with a minimal internal surface area. The Pb(II) recovery rates are notable, with values of 72.4% (SS), 68.6% (C1), 69.7% (C2), 69.6% (Cons), 61.0% (PB), and 72.4% (KP), underscoring the potential of these cost-effective adsorbents for treating Pb(II)-contaminated aqueous streams and contributing to enhanced pollution control measures. Nevertheless, optimization studies are imperative to evaluate the optimal operational conditions and extend the application to adsorb diverse environmental contaminants.

Facile synthesis of flower shaped magnesium ferrite (MgFe2O4) impregnated mesoporous ordered silica foam and application for arsenic removal from water

Magnesium ferrite (MF0.33) impregnated flower-shaped mesoporous ordered silica foam (MOSF) was successfully synthesized in present study. MOSF was added with precursor solution of MF0.33 during MF0.33 synthesis which soaked the materials and further chemical changes occurred inside the pore. Therefore, no additional synthesis process was required for magnesium ferrite impregnated mesoporous ordered silica foam (MF0.33-MOSF) synthesis. MF0.33-MOSF showed higher morphological properties compared to other magnesium ferrite modified nanomaterials and adsorbed arsenic III [As(III)] and arsenic V [As(V)] 42.80 and 39.73 mg/g respectively. These were higher than those of other Fe-modified adsorbents at pH 7. As MOSF has no adsorption capacity, MF0.33 played key role to adsorb arsenic by MF0.33-MOSF. Data showed that MF0.33-MOSF contain about 2.5 times lower Fe and Mg than pure MF0.33 which was affected the arsenic adsorption capacity by MF0.33-MOSF. Adsorption results best fitted with Freundlich isotherm model. The possible mechanism of arsenic adsorption might be chemisorption by electrostatic attraction and inner or outer-sphere surface complex formation.

The Role of Surface Complexes in Ketene Formation from Fatty Acids via Pyrolysis over Silica: from Platform Molecules to Waste Biomass.

Fatty acids (FA) are the main constituents of lipids and oil crop waste, considered to be a promising 2G biomass that can be converted into ketenes via catalytic pyrolysis. Ketenes are appraised as promising synthons for the pharmaceutical, polymer, and chemical industries. Progress in the thermal conversion of short- and long-chain fatty acids into ketenes requires a deep understanding of their interaction mechanisms with the nanoscale oxide catalysts. In this work, the interactions of fatty acids with silica are investigated using a wide range of experimental and computational techniques (TPD MS, DFT, FTIR, in situ IR, equilibrium adsorption, and thermogravimetry). The adsorption isotherms of linear and branched fatty acids C1-C6 on the silica surface from aqueous solution have been obtained. The relative quantities of different types of surface complexes, as well as kinetic parameters of their decomposition, were calculated. The formation of surface complexes with a coordination bond between the carbonyl oxygens and silicon atoms in the surface-active center, which becomes pentacoordinate, was confirmed by DFT calculations, in good agreement with the IR feature at ∼1680 cm 1. Interestingly, ketenes release relate to these complexes' decomposition as confirmed by the thermal evolution of the absorption band (1680 cm-1) synchronously with the TPD peak of the ketene molecular ion. The established regularities of the ketenezation are also observed for the silica-induced pyrolysis of glyceryl trimyristate and real waste, rapeseed meals.

Comparison of arsenate and arsenite removal behaviours and mechanisms from water by Fe[sbnd]La binary composite (hydr)oxides

The present study compares the performances and mechanisms of As(V) adsorption with As(III) removal by a series of FeLa binary composite (hydr)oxides. The As(V) and As(III) adsorption properties were studied by batch adsorption experiments, and their adsorption mechanisms were explored by SEM-EDS, FTIR, XRD and XPS. The FeLa binary composite (hydr)oxides exhibited excellent As(V) removal performances, and their adsorption properties of As(V) were obviously enhanced with increasing La contents. However, their As(III) removal performances were extremely poor, and the increase of Fe contents could not significantly affect As(III) adsorption performances. The adsorption processes of As(V) were rapid, but the As(III) adsorption were slower. The maximum adsorption capacities of As(V) on Fe/La 3:1, Fe/La 1:1, and Fe/La 1:3 were 166.69, 271.65 and 360.81 mg/g, respectively, and those of As(III) were 30.71, 26.44 and 28.64 mg/g, respectively. Solution pH and presence of PO43−, and citrate can clearly influence the removal efficiencies of As(V) and As(III). The predominant mechanisms of As(V) were the formation of LaAsO4 through ligand exchange reactions under all experimental conditions and coprecipitation of La(III) and As(V) under acidic and neutral conditions, while the formation of inner-sphere surface complexes through ligand exchange reactions between Fe–OH groups and As(III) contributed to the As(III) removal. This work emphasizes the different adsorption properties between As(V) and As(III) by FeLa composite (hydr)oxides, and indicates great application potential in As(V) water treatment and the need for pretreatment for As(III) removal, such as pre-oxidation of As(III) to As(V).

Mineralization versus polymerization pathways in heterogeneous Fenton-like reactions

Fenton reaction has been widespread application in water purification due to the excellent oxidation performances. However, the poor cycle efficiency of Fe(III)/Fe(II) is one of the biggest bottlenecks. In this study, graphite (GP) was used as a green carbon catalyst to accelerate Fenton-like (H2O2/Fe3+ and persulfate/Fe3+) reactions by promoting ferric ion reduction and intensifying diverse peroxide activation pathways. Significantly, the carboxyl group on GP anchors iron ions to form GP-COOFe(III) which promote persulfate adsorption to form surface complexes and induce an electron transfer pathway (ETP). While the electron-rich hydroxyl and carbonyl groups will combine to from GP-COFe(II), a reductive intermediate to activate peroxide to generate free radicals (from H2O2 and PDS) or high-value iron [Fe(IV)] (from PMS). Consequently, different pathways lead to distinct degree of oxidation: i) radicals in H2O2/Fe3+/GP prefer to mineralize bisphenol A (BPA) with no selectivity; ii) Fe(IV) in PMS/Fe3+/GP partially oxidizes BPA but cannot open the aromatic ring; iii) ETP in PMS/ or PDS/Fe3+/GP drives coupling reactions to form polymeric products covered on catalyst surface. Thus, rational engineering surface functionality of graphite and selecting proper peroxides can realize on-demand selectivity and oxidation capacity in Fenton-like systems.