Concentration Of Surface Hydroxyl Groups Research Articles

Increasing hydrophobicity of ceramic membranes by post-deposition nitrogen annealing of molecular layer deposition grown hybrid layers

Molecular layer deposition is increasingly used to functionalize the surface of planar and 3D porous substrates. This study explores functionalized ‘alucone’ hybrid layers grown on ceramic substrates to enhance their surface hydrophobicity. The layers were made from trimethyl-aluminum as a precursor with five different alcohols as a co-reactant: aliphatic (ethane-1,2-diol, 2,2-oxydiethanol, 1,6-hexanediol), and aromatic (4-aminophenol, benzene-1,4-diol). After post-deposition annealing in N2 atmosphere at 250 and 350 °C, the changes in the physical properties and the chemical affinity of the layers were studied and compared to those of the as-deposited hybrid layers. Differential thermal analysis of the hybrid layers showed higher decomposition temperatures forthe layers grown from aromatic alcohols than for those grown from aliphatic alcohols. Additionally, Fourier-transform infrared and X-ray photoelectron spectroscopy showed that an increase in annealing temperature decreased the concentrations of surface hydroxyl-groups and caused changes in the carbon-related groups. These results could be correlated to the hydrophobicity of the layers: higher water contact angles (>90°) were measured for annealed samples, compared to those (<90°) of the as-deposited samples grown at 150 °C. These findings confirm that the proposed method of MLD functionalization and post-deposition annealing can be used to tune the surface hydrophobicity of ceramic membranes.

Glycoside-Mediated Enhancement of Stability in Aluminum Oxyhydroxide Nanoadjuvants during Freeze-Drying.

Aluminum-based adjuvants have been indispensable to vaccine potency. However, their effectiveness is difficult to maintain after freeze-drying, which limits the storage and application of aluminum-adjuvanted vaccines. In this study, the impact of freeze-drying on aluminum oxyhydroxide nanorods (AlOOH NRs) was investigated. Freeze-drying led to aggregation and resulted in the loss of the surface hydroxyl content of aluminum adjuvants. To alleviate freeze-drying-induced damage, the potency of different alkyl glycosides as protectants was further evaluated. It was demonstrated that the structural balance of the head and tail of a glycoside was more conducive to protecting AlOOH NRs from aggregation and loss of surface hydroxyl groups. These results underline the proper selection of protectants to protect adjuvants against functional defects caused by freeze-drying, which is important for the stability and efficacy of vaccines and biopharmaceutical products.

Porous Metal Organic Framework (MOF) derived dimorphic (n-ZnO/p-NiO) Z-scheme heterojunction anchored with MWCNTs (ternary nano-architecture): A novel approach for optimization of photodegradation mechanism and kinetics of Congo red (CR) dye

Global efforts to combat water pollution, especially from organic dyes like Congo red, emphasize the use of advanced nanomaterials for sewage purification. Metal-Organic Frameworks (MOFs), known for their crystalline structures and versatile properties, have become pivotal in wastewater treatment research. Integrating MWCNTs into MOF derived composite nanostructures is a strategic advancement, boosting the efficiency of photocatalytic systems and addressing environmental concerns. This study details the synthesis of a novel Z-scheme heterojunction nanocomposite (n-ZnO/p-NiO) incorporating multi-walled carbon nanotubes (MWCNTs), achieved via a solvothermal method using metal-organic framework (MOF) as a template. The study uses XRD, FTIR, FESEM, BET, UV, and PL for comprehensive nanocomposite characterization, offering insights into its structural, morphological, and optical properties. The resultant nanocomposite displays high surface area, sturdy pore arrangement, and consistent morphology. MWCNTs influence crystal growth and optical absorption, enhancing surface hydroxyl group concentration and acting as electron acceptors. This results in decreased photo oxidation and improved overall stability under light exposure in the composite. The composite achieves 92 % Congo red degradation in 60 min under UV light, showcasing superior dye adsorption capacity. This underscores its potential as an efficient photocatalyst for environmental remediation and wastewater treatment.

Poly (ethylene imine)-mediated dihydroxy-functionalized resin with enhanced adsorption capacity for the extraction of boron from salt lake brine

Boron selective resin is a crucial material used for extracting boron from salt lake brine, but the adsorption capacity of resin remains to be improved. In this work, a boron selective resin with high adsorption capacity was created by modifying branched poly (ethylene imine) (PEI) on chloromethyl polystyrene resin, followed by reacting with D-(+)-gluconic acid δ-lactone. The influence of surface hydroxyl content on adsorption capacity of the resin was investigated by varying molecular weights of PEI during modification. The adsorption mechanism of boric acid was explored by changing pH and composition of solution, and by analyzing the adsorption thermodynamic and kinetic behaviors. Furthermore, the selectivity of resin was assessed by the effects of coexisting ions on the adsorption rate of boric acid. The results show that PEI modification effectively increases the content of hydroxyl on the surface of the resin so as to enhance the adsorption capacity of the resin towards boric acid up to 39.4 mg/g. Also, the adsorption rate can still reach up to 75 % even in the presence of 400 times coexisting ion, showing a good selectivity. Furthermore, the adsorption of boric acid is primarily driven by boronate affinity rather than an anion exchange in alkaline solution. Finally, the dynamic extraction of boric acid was carried out, and gives an enrichment factor of up to 39.6 on fixed bed, demonstrating a potential of the resin in the field of boron extraction.

Synthesis Ag-Hollandite by mild route for highly efficient ozone decomposition

Catalytic ozone (O3) decomposition is a promising technology for curbing indoor O3 pollution, whereas its application is limited by the stability and moisture resistance of heterogeneous catalysts. Ag-Hollandite is a capable solution, but its facile synthesis still lacks systematic investigation. In this study, Ag-Hollandite catalysts were prepared using AgMnO4 as the precursor by reflux (AMO-Re), hydrothermal (AMO-HT), and homogeneous (AMO-HR) methods, respectively. The as-prepared samples showed excellent stability under moisture conditions, with the optimal one maintaining an O3 conversion rate of 99.19 % after 100 h. In the characterization results, Ramsdellite (R-MnO2) was identified as an intermediate species in the synthesis. AMO-HR exhibits higher activity due to enhanced active site exposure and weakened adsorption towards *OO species, while reduced surface hydroxyl content was a crucial factor for moisture resistance. This study aims to contribute insights for preparing catalysts by a facile method.

Self-heating photothermal synergistic catalytic decomposition of carcinogenic formaldehyde by α-MnO2 at ambient temperature: Functional roles of surface acidic-basic sites

Formaldehyde is a major pollutant in indoor atmosphere, and the realization of complete mineralization of formaldehyde at room temperature is of great significance and practical demand for improving indoor air quality. Surface acidic-basic sites, as one of the important surface properties that have significant influence on catalytic oxidation of formaldehyde, revealing their functions is beneficial for the development of efficient formaldehyde decomposition materials. Herein, the α-MnO2 acidic-basic sites were regulated and its effects on self-heating photothermal catalytic oxidation of formaldehyde were further contrastive investigated. The acidic-basic sites showed distinct functions: the basic sites exhibited a significant promotion on formaldehyde oxidation; While the acidic sites greatly inhibited the reactivity. Particularly, the basicity enhanced α-MnO2 could reach the 100% conversion of formaldehyde at ambient temperature. Furthermore, the self-heating photothermal mechanism was consonant with the thermal-assisted photocatalysis mechanism, rather than traditional photo-drive thermal catalysis mechanism. The strength of basic sites significantly increased the content of surface hydroxyl groups, and the electron-rich basic sites were favorable for the activation of oxygen, thereby generating more reactive oxygen species for the decomposition of formaldehyde. Moreover, in-situ DRIFTS reveals that the enhancement of basic sites can accelerate the rate oxidation of HCHO to generate formates and carbonates. This work clarified the influence of surface acid-base properties on formaldehyde photothermal decomposition.

Enhancing Surface Hydroxyl Group Modulation on Carbon Nitride Boosts the Effectiveness of Photodynamic Treatment for Brain Glioma.

The effectiveness of photodynamic therapy (PDT) in treating brain gliomas is limited by the solubility of photosensitizers and the production of reactive oxygen species (ROS), both of which are influenced by the concentration of photosensitizers and catalyst active sites. In this study, we developed a controllable surface hydroxyl concentration for the photosensitizer CN11 to address its poor water solubility issue and enhance PDT efficacy in tumor treatment. Compared to pure g-C3N4 (CN), CN11 exhibited 4.6 times higher hydrogen peroxide production under visible light, increased incidence of the n → π* electron transition, and provided more available reaction sites for cytotoxic ROS generation. These findings resulted in a 2.43-fold increase in photodynamic treatment efficacy against brain glioma cells. Furthermore, in vivo experiments conducted on mice demonstrated that CN11 could be excreted through normal cell metabolism with low cytotoxicity and high biosafety, effectively achieving complete eradication of tumor cells.

Effects of Fe(II) bio-oxidation rate and alkali control on schwertmannite microstructure and adsorption of oxyanions: Characteristics, performance and mechanism

Schwertmannite has attracted increasing interest for its excellent sorption of oxyanions such as AsO43−, CrO42−, and Sb(OH)6−. Controlling biomineralization by adjusting the Fe(II) oxidation rate and implementing alkali control can enhance the yield and adsorption performance of schwertmannite. However, the adsorption improvement mechanism is still unclear. The morphology, crystallinity, specific surface area (SSA) and oxyanion adsorption of schwertmannite synthesized with alkali control of solution pH and different Fe(II) oxidation rates were analyzed in this study. The differences in the adsorption mechanisms of As(V), Cr(VI) and Sb(V) on schwertmannite obtained under different synthesis conditions were also studied. Reducing the Fe(II) oxidation rate or maintaining the solution pH through alkali control significantly increased the SSA of schwertmannite and the proportion of outer-sphere sulfate. Alkali-controlled schwertmannite (Sch-C) exhibited superior As(V) and Sb(V) adsorption performance and slightly greater Cr(VI) adsorption than non-alkali-controlled schwertmannite. The As(V) and Sb(V) adsorption capacities of Sch-C greatly improved because the ultra-high SSA increased the surface hydroxyl content and reduced the passivation effect of amorphous precipitates on the mineral surface, allowing continuous sulfate exchange at inner mineral sites. An increased surface hydroxyl content had little effect on Cr(VI) adsorption, but an increased proportion of outer-sphere sulfate caused a slight increase in Cr(VI) adsorption. Sb(V) has a stronger hydroxyl exchange ability than As(V), but due to its octahedral structure, it exchanges only with outer-sphere sulfate on schwertmannite and hardly exchanges with inner-sphere sulfate.

Optimising the acid-base ratio of Mg-Al layered double oxides to enhance CO2 capture performance: the critical role of calcination conditions.

The effect of calcination conditions (ramp rate, calcination temperature and time) on the formation of Mg2Al layered double oxides (Mg2Al LDOs) as well as their CO2 capture performance, has been systematically investigated. This study explores novel insights into the intricate relationship between these calcination conditions and the resulting surface characteristics, which play a vital role in CO2 capture efficiency. Notably, it is revealed that a rapid ramp rate (100 °C min-1) significantly increases surface area and hydroxyl concentration, leading to a 69% increase in CO2 capture efficiency compared to slower ramp rate. Conversely, short calcination times (1 h) and fast ramp rates (100 °C min-1) are observed to compromise CO2 adsorption due to the presence of dehydrated LDHs. A critical acid : base ratio of 0.37, achieved from a fast ramp rate (100 °C min-1) at 400 °C for 2 h, was found as a key threshold for optimising surface properties, effectively balancing favourable hydroxyl and less favourable strong acid sites, thereby maximizing CO2 capture performance.

Novel synergistically effects of palladium-iron bimetal and manganese carbonate carrier for catalytic oxidation of formaldehyde at room temperature

The elimination of formaldehyde at room temperature holds immense potential for various applications, and the incorporation of a catalyst rich in surface hydroxyl groups and oxygen significantly enhances its catalytic activity towards formaldehyde oxidation. By employing a coprecipitation method, we successfully achieved a palladium domain confined within the manganese carbonate lattice and doped with iron. This synergistic effect between highly dispersed palladium and iron greatly amplifies the concentration of surface hydroxyl groups and oxygen on the catalyst, thereby enabling complete oxidation of formaldehyde at ambient conditions. The proposed method facilitates the formation of domain-limited palladium within the MnCO3 lattice, thereby enhancing the dispersion of palladium and facilitating its partial incorporation into the MnCO3 lattice. Consequently, this approach promotes increased exposure of active sites and enhances the catalyst's capacity for oxygen activation. The co-doping of iron effectively splits the doping sites of palladium to further enhance its dispersion, while simultaneously modifying the electronic modification of the catalyst to alter formaldehyde's adsorption strength on it. Manganese carbonate exhibits superior adsorption capability for activated surface hydroxyl groups due to the presence of carbonate. In situ infrared testing revealed that dioxymethylene and formate are primary products resulting from catalytic oxidation of formaldehyde, with catalyst surface oxygen and hydroxyl groups playing a crucial role in intermediate product decomposition and oxidation. This study provides novel insights for designing palladium-based catalysts.

Effect of isomorphic replacement of palygorskite on its heavy metal adsorption performance

Isomorphism is a common phenomenon in clay minerals, which is one of the main reasons for the change of mineral chemical composition and physical and chemical properties. In this study, four kinds of palygorskite with different degrees of isomorphic replacement of octahedral cations were selected. The microstructure and surface-interface properties of different Mg2+/Al3+ palygorskite were analyzed by X-ray diffraction, infrared spectroscopy, N2 adsorption-desorption method, X-ray fluorescence spectroscopy and other characterization methods, and the effects of isomorphic replacement on microstructure such as Mg content and surface-interface properties such as hydroxyl concentration and acid content were discussed. Taking Cu2+ as the target pollutant, the adsorption capacity of different palygorskite to Cu2+ was measured and discussed. Combining the surface hydroxyl concentration and acid amount of palygorskite, as well as the concentration, time and temperature of the reaction system, the rule of adsorption of the four palygorskite for Cu2+ was Mg-rich palygorskite (a-ATP) &amp;gt; palygorskite with equal Mg and Al (c-ATP) &amp;gt; Al-rich palygorskite (d-ATP) &amp;gt; palygorskite with the most Mg (b-ATP), demonstrating that when Mg was partially replaced by Al, palygorskite contained appropriate hydroxyl concentration and acid amount, resulting in the best adsorption effect for Cu2+ (29.2 mg/g). It is of great significance for resource utilization of palygorskite to reveal the regularity of heavy metal adsorption by isomorphic replacement of palygorskite.

Peroxymonosulfate Activation by Facile Fabrication of α-MnO2 for Rhodamine B Degradation: Reaction Kinetics and Mechanism.

The persulfate-based advanced oxidation process has been an effective method for refractory organic pollutants' degradation in aqueous phase. Herein, α-MnO2 with nanowire morphology was facially fabricated via a one-step hydrothermal method and successfully activated peroxymonosulfate (PMS) for Rhodamine B (RhB) degradation. Influencing factors, including the hydrothermal parameter, PMS concentration, α-MnO2 dosage, RhB concentration, initial pH, and anions, were systematically investigated. The corresponding reaction kinetics were further fitted by the pseudo-first-order kinetic. The RhB degradation mechanism via α-MnO2 activating PMS was proposed according to a series of quenching experiments and the UV-vis scanning spectrum. Results showed that α-MnO2 could effectively activate PMS to degrade RhB and has good repeatability. The catalytic RhB degradation reaction was accelerated by increasing the catalyst dosage and the PMS concentration. The effective RhB degradation performance can be attributed to the high content of surface hydroxyl groups and the greater reducibility of α-MnO2, and the contribution of different ROS (reactive oxygen species) was 1O2 > O2·- > SO4·- > ·OH.

Mechanism for the effects of surface chemical composition and crystal face on the wettability of α-quartz surface

Quartz is a ubiquitous matter in natural rock and industrial production, and the wetting property of quartz surface plays a critical role in determining numerous industrial processes. However, the key mechanism for the effects of surface chemical composition (based on surface pretreatment) and crystal face on the wettability of quartz surface remains vague. Herein, by applying an advanced atomic force microscopy (AFM), we measured the contact angles of liquids on three common crystal faces of α-quartz after different pretreatments. The time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis and molecular dynamics (MD) simulations were further conducted to uncover the microscopic mechanism involved. It is found that the surface pretreatment does significantly affect the wettability of α-quartz faces, mainly because of the variation in surface hydroxyl concentration after different surface pretreatments. The magnitude of change in contact angle after distinct pretreatments is also affected by the liquid property. After certain pretreatments, although there is no difference in the wettability of different faces, the inherent atomic arrangement of crystal faces still causes discrepancies in other interface properties, e.g., liquid structure, diffusion coefficient of liquid molecule. The reasonable pretreatments of α-quartz for a range of applications are recommended based on the current findings.

Heterogeneous Epoxidation of Microcrystalline Cellulose and the Toughening Effect toward Epoxy Resin

Microcrystalline cellulose (MCC) is regarded as a potential filler in the fabrication of epoxy composites. However, MCC’s hydrophilic nature and strong hydrogen bonds caused by abundant surface hydroxyl groups greatly weaken its compatibility with the epoxy resin. In addition, it remains a challenge to efficiently and heterogeneously modify MCC surface hydroxyl groups. In this work, MCC was epoxidized heterogeneously with a phase-transfer catalyst. Results indicated that 4.48% (by mass) or 58.15% (by coverage) of the hydroxyl groups on MCC was modified. The dispersibility of epoxidized MCC (EP-MCC) in the epoxy resin was significantly improved. At the same time, EP-MCC showed the ability to interact with the epoxy network covalently, improving the interface interactions, indicating the simultaneous enhancement of the modulus and the toughness. As a result, this heterogenous epoxidation method showed high efficiency in reducing the surface hydroxyl content of MCC, endowing it with a bright future in industrial applications of epoxy composites.

The insight into the synergistic effect between goethite and birnessite on the degradation of tetracycline

The environmental fate of tetracycline (TC) has been documented closely related to goethite (α-FeOOH) or birnessite (δ-MnO2) in soil, while their synergistic effect on TC transformation remains unclear. Herein, a series of δ-MnO2@FeOOH were synthesized to investigate the interaction between α-FeOOH and δ-MnO2 for TC transformation. The results showed that the higher specific surface area and larger amount of surface hydroxyl content were found in δ-MnO2@FeOOH than those of the bulk α-FeOOH and δ-MnO2, enhancing the adsorption capacity for TC. The α-FeOOH introduction was conducive to the electron transfer efficiency and the increase of Mn(III) species, thus, forming more reactive oxygen species (ROSs) for the oxidation of TC. Moreover, the comparative study of the degradation of the common organic pollutants in soli over δ-MnO2@FeOOH indicated the synergistic effect of δ-MnO2 and α-FeOOH showed selectivity in the TC degradation. In addition, 20%δ-MnO2@FeOOH displayed highest removal percentage of 98% for TC (10.0 mg/L) and the removal performance first increased and then decreased as δ-MnO2 loading on the surface of α-FeOOH from 10% to 70%. This study provides a new insight into the transformation of organic pollutant under the interaction between α-FeOOH and δ-MnO2.

Correlations between residual stress and water diffusion in silica glass at low temperatures

AbstractResidual stress profiles in silica glass were measured after water diffusion treatment under 47.33 kPa (355 Torr) water vapor at 350°C and 650°C. Earlier, it was found that water solubility in silica glass exhibited peculiar time dependence: Solubility increased with time exceeding the normal water solubility expected from higher temperatures. Then, the water solubility decreased with time. It was hypothesized that the stress induced by water diffusion and its subsequent relaxation is responsible for the phenomenon. Residual surface stress generation in silica glass was found to correlate closely with surface hydroxyl concentration, systematically increasing until eventual surface stress relaxation results in stress decrease for treatments beyond 265 hours at 650°C. This observation validates previous theories of time dependent diffusivity in silica glass.

Nucleation and growth of molybdenum disulfide grown by thermal atomic layer deposition on metal oxides

To enable greater control over thermal atomic layer deposition (ALD) of molybdenum disulfide (MoS2), here we report studies of the reactions of molybdenum hexafluoride (MoF6) and hydrogen sulfide (H2S) with metal oxide substrates from nucleation to few-layer films. In situ quartz crystal microbalance experiments performed at 150, 200, and 250 °C revealed temperature-dependent nucleation behavior of the MoF6 precursor, which is attributed to variations in surface hydroxyl concentration with temperature. In situ Fourier transform infrared spectroscopy coupled with ex situ x-ray photoelectron spectroscopy (XPS) indicated the presence of molybdenum oxide and molybdenum oxyfluoride species during nucleation. Density functional theory calculations additionally support the formation of these species as well as predicted metal oxide to fluoride conversion. Residual gas analysis revealed reaction by-products, and the combined experimental and computational results provided insights into proposed nucleation surface reactions. With additional ALD cycles, Fourier transform infrared spectroscopy indicated steady film growth after ∼13 cycles at 200 °C. XPS revealed that higher deposition temperatures resulted in a higher fraction of MoS2 within the films. Deposition temperature was found to play an important role in film morphology with amorphous films obtained at 200 °C and below, while layered films with vertical platelets were observed at 250 °C. These results provide an improved understanding of MoS2 nucleation, which can guide surface preparation for the deposition of few-layer films and advance MoS2 toward integration into device manufacturing.

Effect of reduction degree of Ni-phyllosilicate on the catalytic performance for CO2 methanation: Regulation of catalyst structure and hydroxyl group concentration

In order to reveal the interrelationship among reduction degree and catalyst structure as well as surface hydroxyl group concentration of Ni-phyllosilicate, four different reduction temperatures of 550, 600, 700 and 800 °C were used. The results showed that low-temperature reduction could lead to high catalytic activity for CO2 methanation. In detail, the low-temperature partial reduction catalyst treated at 550 °C (Ni/S-550R) obtained the smallest Ni particle size, the highest specific surface area and the largest pore volume, which were beneficial to the chemisorption and activation of H2. In addition, the unreduced nickel phyllosilicate also provided abundant hydroxyl groups to facilitate the activation of CO2. With the increasing of reduction temperature, the reduction degree increased quickly; however, the TEM and XRD results showed that the Ni sintering was serious reduced at 700 or 800 °C. What's more, the SiO2 support also transferred from amorphous to crystalline at high reduction temperature with the significant collapse of pore structure. In all, a series of characterization results displayed that the low-temperature reduction of Ni-phyllosilicate catalyst exhibited strong H2 and CO2 chemisorption and activation capacity compared with the high-temperature-reduction ones leading to high CO2 methanation activity.

Surface hydroxyl modification for silicate-stabilized low-melting glassy tellurite adhesive enabling low resistance of silver conductive paste

With the booming development of new electronic devices, the demand of high-end silver conductive paste has been sharply increased. In this study, we achieve low sheet resistance silver paste by using silicate stabilized glassy tellurite adhesive with hydrophobic surface through effective surface modification. We developed a wet milling process and employed lauryl gallate to remove surface hydroxyl content of micro-scale silicate-containing tellurite low-melting glasses. This surface modification can effectively prevent agglomeration caused by hydroxyl condensation, meanwhile eliminate defects of sintered silver layer. The introduction of silicate to tellurite glassy adhesive is used to improve water and alkaline resistance and corrode wafer surface to enhance its contact with silver. A sintered silver layer with low sheet resistance of 35.6 mΩ/□ was obtained, despite only 1–3 μm size silver particles are used and sintered at relatively low temperature around 500 °C. This research provides a practical path-forward of improving overall performance of metal conductive pastes from a new angle of innovating glassy adhesive.

Effects of synthesis temperature on ε-MnO2 microstructures and performance: Selective adsorption of heavy metals and the mechanism onto (100) facet compared with (001)

The heavy-metal adsorbent ε-MnO2 was produced through a simple, one-step oxidation-reduction reaction at three different synthesis temperatures (25 °C, 50 °C and 75 °C) and their morphology and chemical-physical properties were compared. Of the three materials, MnO2-25 had the largest specific surface area and the highest surface hydroxyl concentration. Its optimal performance was demonstrated by batch adsorption experiments with Pb2+, Cd2+ and Cu2+. Of the three metals, Pb2+ was adsorbed best (339.15 mg/g), followed by Cd2+ (107.50 mg/g) and Cu2+ (86.30 mg/g). When all three metals were present, Pb2+ was still absorbed best but now more Cu2+ was adsorbed than Cd2+. In order to explore the mechanism for the inconsistent adsorption order of Cd2+ and Cu2+ in single and competitive adsorption, we combined experimental data with density functional theory (DFT) calculations to elucidate the distinct adsorption nature of MnO2-25 towards these three metals. This revealed that the adsorption affinity of the (100) facet was superior to (001), and since the surface complexes were also more stable on (100), this facet was most likely determining the adsorption order for the single metals. When the metals were present in combination, Pb2+ preferentially occupied the active adsorption sites of (100), forcing Cu2+ to be adsorbed on the (001) facet where Cd2+ was only poorly bound. Thus, the adsorption behavior was affected by MnO2-25 surface chemistry at a molecular scale. This study provides an in-depth understanding of the adsorption mechanisms of the heavy metals on this adsorbent and offers theoretical guidance for production of adsorbent with improved removal efficiency.