Surface Chemical Adsorption Research Articles

Utilization of orange peel waste for activated carbon production and its application in particleboard for formaldehyde emission reduction

AbstractActivated carbon (AC) is valued for its large surface area, porosity, and chemical adsorption properties, making it suitable for a wide range of industrial applications. Its most common sources are coconut shells, wood, and coal – all of which are costly or harmful to the environment. It is thus important to finding sustainable feedstock, such as agricultural waste. Inexpensive materials like waste orange peel have been used in the production of AC. This study explores the synthesis of AC from orange peel waste through phosphoric acid (H3PO4) activation for potential applications in reducing volatile organic compounds such as formaldehyde emissions in particleboard production. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nitrogen adsorption/desorption isotherms, and Fourier transform infrared (FTIR) spectroscopy were used to examine AC. The Brunauer–Emmett–Teller (BET) surface area of AC was 497 m2·g⁻¹. The addition of AC to urea‐formaldehyde (UF) adhesive enhanced cross‐linking and condensation reactions, improving the mechanical and physical properties of particleboards without compromising integrity. The effects of AC on formaldehyde emissions were assessed at 0 and 3 months. Compared to the control group, particleboards with AC showed a 28.98% reduction in free formaldehyde emissions at 0 months and a 45.25% reduction at 3 months. Activated carbon derived from orange peels can thus improve particleboard properties while reducing formaldehyde emissions in an environmentally sustainable way.

Surface electric fields-enhanced biochar: A dual-action adsorbent and PMS activator for sulfamethoxazole removal

Integrating adsorption with advanced oxidation processes offers significant advantages over conventional single-stage wastewater treatment methodologies. Herein, this study successfully synthesized nitrogen-boron codoped metal-free biochar at 700 °C (700NBBC). 700NBBC effectively eliminates sulfamethoxazole (SMX) from water through a synergistic adsorption-oxidation process, showcasing robust resistance to interference and broad pH tolerance. Characterizations and experimental outcomes indicate that 700NBBC primarily adsorbs SMX through a monolayer surface chemical adsorption mechanism and activates persulfate (PMS) to oxidize SMX via a non-radical mechanism, which includes the generation of singlet oxygen (1O2) and electron transfer processes. Density functional theory calculations elucidate that N and B doping regulate the local electronic environment at biochar surface, enhancing the adsorption energy between biochar and PMS while effectively catalyzing PMS cleavage to generate 1O2. This research offers fresh perspectives on the critical role of heteroatom doping in regulating reactive oxygen species generation within biochar.

Oxidation of Toluene over the Pt-Embedded Mesoporous CeO2 Hollow Nanospheres with Advanced Catalytic Performances.

In this study, the novel Pt-embedded mesoporous CeO2 hollow nanospheres (Pt-MS-CeO2-H) with varying Pt contents (0.5-3.0 wt %) were facilely prepared. The Pt nanoparticles were one-pot embedded within the mesoporous shell of Pt-MS-CeO2-H and assisted with the reduction Ostwald ripening process. The traditional preparation methods often face challenges, such as the uneven distribution or aggregation of nanoparticles, as well as difficulty in maintaining high catalytic activity at low Pt content. Compared with the traditional supported Pt/MS-CeO2 catalyst, the embedding strategy facilitated precise control over the position, distribution, and uniformity of Pt nanoparticles within the CeO2 mesoporous shell. Additionally, the encapsulation process of Pt nanoparticles played a pivotal role in generating oxygen vacancies and activating surface chemical adsorption of oxygen. Resultantly, the toluene oxidation performances of 1Pt-MS-CeO2-H catalyst showed much lower T90 (171 °C) than 1Pt/MS-CeO2 (311 °C). To elucidate the underlying reasons, in situ diffuse reflectance infrared Fourier transform spectroscopy of toluene oxidation was employed to identify the reaction intermediates and pathways over these catalysts. In summary, the Pt-embedded mesoporous CeO2 hollow nanosphere catalysts were considered as potential candidates when designing high-performance toluene catalytic oxidation catalysts.

Biomass betulin-based porous aromatic frameworks nanomicrospheres as adsorbents for reversible capture of iodine

Betulin with a modifiable hydroxyl group and a rigid backbone is a kind of natural triterpene product that extracted from white barked birch bark with up to 30 % of its dry weight. Herin, we prepared a series of betulin-based porous aromatic frameworks (BEPAFs) nanomicrospheres by [Rh(nbd)Cl]2 polymerization or Sonogashira-Hagihara coupling reaction for iodine vapor capture and adsorption. The resulting BEPAFs nanomicrospheres presented perfect thermal stability and high specific surface areas that up to 324.6 m2 g−1, 506.3 m2 g−1 and 320.5 m2 g−1 for BEPAF-1, BEPAF-2 and BEPAF-3, respectively. Based on the above characteristics, the BEPFAs nanomicrospheres showed an excellent iodine capture performance with the volatile iodine capture ability reached 3.79 g g−1 and iodine adsorption in cyclohexane solution up to 389.9 mg g−1. The iodine capture behavior is consistent with the pseudo-second-order model, indicating that the iodine adsorption process of BEPAFs microspheres belongs to multilayer heterogeneous surface chemical adsorption. Furthermore, the BEPFAs nanomicrospheres could maintained 88.26 % of the absorption capacity after four cycles that endow them a great potential in practical application. This research provides a facile synthesis of biomass porous aromatic framework nanomicrospheres adsorbents based on the natural product.

Bridging the Adsorption Data and Adsorption Process by Introducing a Polynomial Structure To Accurately Describe IUPAC Isotherms, Stepwise Isotherms, and Stepwise Breakthrough Curves.

Porous heterogeneous adsorbents, those composed of multiple pore structures and surface chemical adsorption sites, can result in various gas or vapor adsorption isotherms, including five types of IUPAC adsorption isotherms and stepwise adsorption isotherms that have been difficult to model using a single adsorption equilibrium model. The limitation of the above equilibrium model further restricts the calculations of complex stepwise breakthrough curves. To bridge the adsorption data and adsorption process, it is important to first develop a simple model or method to describe these isotherms of various complex adsorption systems. In this work, assuming that the effect of the diffusion rate can be neglected under the static condition and the adsorption process is discontinuous, the number of adsorption isotherm inflection points can be used to represent the changed number of adsorption interactions. With the introduction of the polynomial structure, a series of empirical or semi-empirical polynomial adsorption models were developed. The N-site polynomial Langmuir-Freundlich equation could accurately fit common type I, II, III, IV, and V adsorption isotherms and complex stepwise adsorption isotherms covering various adsorbates, such as volatile organic compounds (VOCs), toxic industrial chemicals (TICs), water vapor, and carbon dioxide, as well as different adsorbents, such as metal/covalent organic frameworks (MOFs/COFs), zeolites, and porous carbons. Similarly, the introduction of a polynomial structure, such as the N-site polynomial Yoon-Nelson equation, was also successful in the description of interesting stepwise breakthrough curves. This work provides a more accurate adsorption equilibrium model to characterize all types of isotherms. As a foundation model, it is expected to be used to simulate the gas-solid adsorption process inside the fixed and fluidized beds packed with porous adsorbents.

The enhanced responsivity and response speed of SnO2 visible-blind transparent photodetectors via the SiO2 passivation layer.

Recently, transparent ultraviolet (UV) photodetectors have gained wide attention for their giant potential in integrated transparent electronics applications. SnO2 films as a common candidate for visible-blind transparent ultraviolet photodetectors have attracted increasing attention. In this work, high-performance visible-blind transparent UV photodetectors based on SnO2 thin film and a SiO2 passivation layer were successfully synthesized by the sol-gel spin coating method for the first time. The obtained SnO2/SiO2 hybrid device has a transmittance of nearly 80% in the visible band at 400-700 nm and demonstrates a high responsivity of 769 mA W-1 and a detection sensitivity of 1.24 × 1014 Jones under UV light illumination. The UV-C/UV-A rejection ratio is greater than 106, indicating that the device has good photo-selectivity. In addition, after the introdution of the SiO2 layer, the response speed is 2 times higher than that of pure SnO2. The presence of the SiO2 layer reduces the exposed area of SnO2, passivates the oxygen vacancies on the surface of SnO2 and inhibits the surface chemical adsorption. The above results provide a new perspective for improving the performance of SnO2 thin film for visible-blind transparent ultraviolet photodetectors.

Combined experimental and DFT study on the adsorption of congo red dye using self-assembled hierarchical microspheres of lanthanum hydroxide

Self-assembled hierarchical microspheres of lanthanum hydroxide (La(OH)3) were used to investigate the adsorption of the azo-dye Congo Red (C.R.) in an aqueous medium. The versatile coordination chemistry of lanthanum ions makes them very efficient in adsorption processes involving organic ligands. The microspheres were synthesized using the reaction-diffusion framework (RDF) at ambient temperature, which consists of diffusing a concentrated ammonia solution onto an agar hydrogel matrix containing the dissolved lanthanum salt. The microspheres, which emerged with distinct Liesegang bands ranging in size from ∼300 nm to ∼70 µm, demonstrated rapid adsorption, reaching equilibrium within 15 min, with optimal adsorption of 395 mg g–1 at pH 6 and 30 °C. The kinetic and thermodynamic data were analyzed and fitted to a pseudo-second-order equation and the Sips model. The adsorption mechanism, driven by the dye's structure, the adsorbent's surface chemistry, and the medium, involves complex interplays of electrostatic attractions, physisorption, and chemisorption, with water playing a pivotal role. The positive enthalpy of adsorption extracted from a Sips isotherm, diverging from Langmuir behavior, and FTIR spectral comparisons pre- and post-adsorption provide empirical insights. Density functional theory (DFT) calculations, complemented by implicit solvation models, reveal significant solvation effects on the adsorption enthalpy of the sulfonate group of C.R. on the La(OH)3 surface, highlighting the solvent's vital role. The adsorption enthalpy of +62.63 kJ mol–1 closely aligns with the primary termination of the lanthanum hydroxide surface by water molecules. Remarkably, the bond length between the surface lanthanum and water's oxygen undergoes a significant shift when bonded to the sulfonate group. This study offers a deeper understanding of C.R. dye adsorption dynamics, emphasizing both experimental findings and theoretical insights, underscoring the complex interplay of forces and the central role of water in the process.

Experimental study on microstructural modification of coal by liquid CO2 extraction

Liquid CO2 injection into coal seam for CH4 displacement is one of the important means to strengthen gas extraction and carbon sequestration in recent years. After liquid CO2 is injected into coal seam, physical and chemical interactions occur with coal through the process of “liquid phase seepage-phase transformation supercharging-gas–liquid mass transfer”, and microscopic characteristics of coal such as pore distribution, surface chemical properties and adsorption characteristics change. Three kinds of coal samples with different degrees of metamorphism were selected as research objects, theoretical analysis, numerical simulation and experimental testing were combined to carry out research on the modification of coal body by liquid CO2 extraction. The results show that with the increase of extraction pressure, the diffusion rate of small organic molecules in coal increases, which is conducive to the dissolution of small organic molecules; In larger pores, the contact area between liquid CO2 and pore surface increases, and small molecular organic matter is easy to precipitate; The infrared spectra of raw coal and residual coal after extraction are basically the same, and the absorption peak intensity is significantly different, liquid CO2 extraction does not significantly damage the macromolecular structure of coal. The research results have important reference value for liquid CO2 anti-reflection coal seam and geological storage.

A novel MnTi mixed oxide catalyst engineered by metal–organic framework precursor for enhancing NOx removal performance

In this research, MnTi metal–organic frameworks (MnTi‐MOFs) were successfully prepared, and derived catalysts were innovatively applied to the removal of NOx by selective catalytic reduction with NH3 (NH3‐SCR). The test results show that the one‐step controllable synthesis of MnTi‐MOFs material is achieved through adjusting the Mn/Ti molar ratios and the proportion of metal to organic ligands, in which the ratio of organic ligands is vitally significant for the synthesis of MnTi‐MOFs (MnTi‐MOFs can only be synthesized with the ligand to metal molar ratio in the range of 3–4). Owing to the special heterogeneity of MOFs, the catalyst sample derived from the MnTi‐MOFs precursor prepared with suitable raw material ratio exhibits the best SCR performance. Series of characterization analyses show that the catalysts derived from MOFs precursors with ordered lattice structure exhibit an appropriate surface chemical adsorption oxygen, an increased Mn4+/Mnn+ content, and enhanced acidity of the surface of the sample. This research affords an innovative method to the controllable preparation of dual metal MOFs and expands the development of catalysts in the field of low‐temperature de‐NOx.

Hydrogen bonding donor/acceptor active sites exposed on imide-functionalized carbon dots aid in enhancing arsenic adsorption performance

During the arsenic (As) adsorption process, amino-functionalization has been widely considered as one of the effective adsorbents optimization methods, while this study reveals that imide functional groups also play a non-negligible role. Herein, magnetic carbon dots (CDs) equipped with imide (FeCD-NH) or amino functional groups (FeCD-NH2) were synthesized to deduce the relationship between different configurations of amino-like functional groups and As. The results showed that FeCD-NH exhibited extraordinary As(V) adsorption behavior (with 97.80 % As(V) removal within 5 min), outperformed that equipped with amino functional groups (FeCD-NH2). An array of advanced characterization techniques and density functional theory (DFT) calculation collectively revealed a dual-configuration hydrogen bond synergistic mechanism of FeCD-NH toward As(V). Different from monomorphic hydrogen bond of amino functional group, imide functional group forms abundant adsorption sites through dual-configuration hydrogen bonds to realize the ultrafast adsorption of As(V). In addition, FeCD-NH can remove As(V) from other more complex water matrices to levels below the World Health Organization (WHO) drinking water standards and the Chinese surface water standards. Therefore, this work provides a promising strategy for As decontamination by fine-tune the surface chemistry of adsorbents.

Advancements in theoretical and experimental investigations on diamane materials.

Technology-driven modern civilization demands new materials as its backbone. Consequently, based on intense research, a promising candidate, diamane, which is a two-dimensional (2D) form of diamond with a bilayer sp3 carbon nanostructure, has been proposed and recently achieved from bi-layer graphene (BLG) or few-layer graphene (FLG) through high-pressure technology or surface chemical adsorption. This material has been reported to possess a tunable bandgap, excellent heat transfer ability, ultralow friction, and high natural frequency, which can be a potential asset for cutting-edge technological applications, including quantum devices, photonics, nano-electrical devices, and even space technologies. In this review, following the history of the development of diamane, we summarize the recent theoretical and experimental studies on diamane in its pristine form and functionalized with substituents (H-, F-, Cl-, and OH-) in terms of atomic structure, synthesis strategies, physical properties, and potential technological applications. Also, the current challenges and future opportunities for the further development of diamane are discussed. As a young material with great potential but limited experimental research, there is still great space for its exploration.

Molecular Dynamics Beyond the Monolayer Adsorption as Derived from Langmuir Curve Fitting.

Langmuir adsorption model is a classic physical-chemical adsorption model and is widely used to describe the monolayer adsorption behavior at the material interface in environmental chemistry. Traditional adsorption dynamic modeling solely considered the surface physiochemical interaction between the adsorbent and adsorbate. The surface reaction dynamics resulting from the heterogeneous surface and intrinsic electronic structure of absorbents were rarely considered within the reported adsorption experiments. Herein, by employing the chlorine hybrid graphene oxide (GO-Cl) to adsorb Ag+ in an aqueous solution, complicated molecular dynamics significantly deviated from the monolayer adsorption mechanism, as suggested by Langmuir adsorption curve fitting, has been elucidated down to atomic scale. In the time-dependent Ag adsorption experiments, both Ag single atoms and Ag/AgCl nanoparticle heterostructures are observed to be formed sequentially on GO-Cl. These observations indicate that for the surface adsorption dynamics, not only the surface chemical adsorption process involved but also photoreduction and the C-Cl bond cleavage reaction has been heavily engaged within the GO-Cl interface, suggesting a much more complicated vision rather than the monolayered adsorption algorithm as derived from curve fitting. This study uses GO-Cl as a simple example to disclose the complicated adsorption dynamic process underneath Langmuir adsorption curve fitting. It advocates the necessity of imaging the interfacial atomic-scale dynamic structure with high-resolution microscopy techniques in modern adsorption studies, rather than simply explaining the adsorption dynamics relying on the curve fitting results due to the complicated physiochemical reactivity of the adsorbents.

Assessment of the selective flotation of calcite, apatite and quartz using bio-based collectors: Flaxseed, nigella, and olive oils

• Bio-based collectors were tested in a FAp/Cal/QTZ flotation system. • The collector’s dosage and composition control the adsorption. • pH and mineral dissolution impact the adsorption mechanism. • The collectors had more affinity towards calcite . • Flaxseed oil collector allowed the recovery of 95.7% calcite. Bio-based flotation reagents are of great interest considering their low-cost, abundance, and sustainability. This study evaluates the performance of saponified vegetable oils as collectors in phosphate ores’ flotation. Olive, nigella, and flaxseed oils were elected for their fatty acid composition and their local availability. Prior to saponification, the oils’ acidity index, saponification value, and fatty acids profile were determined. Surface chemical characterization, adsorption quantification and isotherms, zeta potential, and wettability assessments were conducted on bare and treated pure fluorapatite, calcite, and quartz. At low collector dosages, results revealed the chemical adsorption of the synthesized collectors on calcite and fluorapatite surfaces. With increasing dosages, the collectors’ molecules precipitated at the calcium-bearing minerals’ surface as calcium dicarboxylates salts then as micelles of fatty acids. Furthermore, flaxseed’s soap exhibited higher adsorption densities and significant contact angle increases on the surface of calcite (8.20 mg/m 2 and +32.93°) compared to fluorapatite (2.43 mg/m 2 and +3.65°). Moreover, collectors’ adsorption on the surface of quartz was minimal. Accordingly, flaxseed’s soap, served as an efficient calcite collector in phosphate flotation while including phosphoric acid for apatite depression. It enabled the recovery of up to 95.7% calcite at pH 12.

Effective removal of anionic dyes from aqueous solutions by novel polyethylenimine-ozone oxidized hydrochar (PEI-OzHC) adsorbent

The adsorption behavior of the anionic dyes Remazol Brilliant Blue R (RBBR) and Reactive Black 5 (RB5) from aqueous solutions by polyethylenimine ozone oxidized hydrochar (PEI-OzHC) was investigated. The adsorption capacities of both dyes increased with functionalization of PEI in the hydrochar adsorbent. The results of surface characterization (FTIR, BET, TGA, elemental analysis, and SEM) showed that PEI modification greatly enhanced the adsorbent surface chemistry with a slight improvement of adsorbent textural properties. In addition, the adsorption kinetics data showed an excellent adsorption efficiency as reflected in the high removal percentages of the anionic dyes. The Isotherm results indicated that RBBR and RB5 dye adsorption occurred via monolayer adsorption, and chemisorption was the rate-controlling step. The PEI-OzHC adsorbent possesses higher maximum Langmuir adsorption capacity towards RBBR (218.3 mg/g) than RB5 (182.7 mg/g). This increase in adsorption capacity is attributed to the higher number of functional groups in RBBR that interact with the adsorbent. This study reveals the potential use of adsorbents derived from pine wood hydrochar in municipal as well as industrial wastewater treatment. Furthermore, surface chemistry modification is proven as an effective strategy to enhance the performance of biomass-derived adsorbents.

In English

Interfacial phenomena at a surface of porous and highly disperse adsorbents in the systems containing strongly and weakly bound and unbound liquids depend strongly on the confined space effects. These effects as well as the temperature behavior of liquids located in pores or voids between nanoparticles depend on many factors. They are the pore size distributions, pore volume, specific surface area, surface chemistry of adsorbents, chemical structure and molecular sizes of adsorbates, accessibility of pores vs. probe molecule sizes, as well as textural instability of adsorbents. This instability can appear, e.g., as compaction of fumed oxides under action of liquid adsorbates, especially water, or due to mechanochemical activation. The aim of this study is to analyze features of the interfacial phenomena upon interactions of fumed oxides (silica, alumina, alumina/silica/titania) and porous silicas (silica gels and precipitated silica) with polar (water, dimethyl sulfoxide), weakly polar (chloroform), and nonpolar (n-decane, aromatic benzene and toluene) liquid adsorbates depending on the morphological and textural characteristics of the adsorbents, various adsorbate characteristics, and temperature. The observed effects as well as related phenomena are important because they can differently influence the efficiency of practical applications of adsorbents under various conditions (temperature, pressure, concentrations) depending on the characteristics of adsorbents and adsorbates (liquids, solvents and solutes).

A Study on the Effects of Surface Energy and Topography on the Adhesive Bonding of Aluminum Alloy

The bonding properties of adhesives are mainly affected by surface roughness, topography and chemical adsorption. In this paper, we studied the effects of surface pretreatment of Al 2024-T3 (bare) in terms of surface roughness, topography and surface free energy. Surface pre-treatment included solvent cleaning, FPL etching, PAA and CAA treatment. The surface energy and roughness of the aluminum surface were significantly increased by the anodizing treatment. Single lap shear and fatigue tests were performed to investigate bonding properties and durability. The evaluation revealed that the surface energy and surface roughness resulting from the aluminum surface treatment had a significant impact on bonding properties and durability. PAA treated surfaces had the highest bonding strength, and CAA treated surfaces had superior bonding retention performance in hot water or salt spray environments. The results of the fatigue test most clearly demonstrated how the surface pretreatment of the aluminum alloy differently affected bonding performance.

Facile Modification of Biochar Derived from Agricultural Straw Waste with Effective Adsorption and Removal of Phosphorus from Domestic Sewage

In recent decades, straw waste is the major byproduct around agriculture that has become one of the factors of environmental pollution. The purpose of this study is to reuse waste straw to develop a new green and highly efficient biomass-based adsorbent for phosphorus removal. To attain this aim, Mg–Al bimetallic oxide/straw fiber (Mg–Al/SF) with hierarchical structure was successfully synthesized by hydrothermal method using waste straw as the biomass carbon precursor and Mg–Al/SF was applied as adsorbent in the removal of phosphorus from wastewater. The morphology, composition and structure of the adsorbent was well supported by several characterizations. The prepared biomass-based adsorbent showed outstanding adsorption performance. Maximum adsorption capability of Mg–Al/SF towards phosphorus from the Langmuir isotherm model was fitted out to be 89.37 mg/g. The related kinetics and isotherm study for the adsorption process were explored in detail. The proposed adsorbent exhibited good reusability that the removal of phosphorus remained above 72% after 5 cycles. In addition, thermodynamic study was carried out to further investigate the phosphorus removal mechanism, which was the synergistic combination of surface adsorption and chemical adsorption. The removal of total phosphorus in actual domestic sewage (Total phosphorus, TP, 0.8–1.1 mg/L) were investigated. The results indicated that the prepared Mg–Al/SF has excellent TP adsorption and recycling performance, and the adsorption and stability performance are significantly higher than that of the commercial activated carbon. The interactions between biomass material with large surface area and metal oxide provides great potential for the real application in the water treatment. Furthermore, it also presents a feasible and efficient practical example of increasing the use of agricultural waste.

Surface modification of activated carbon fiber by low-temperature oxygen plasma: Textural property, surface chemistry, and the effect of water vapor adsorption

The effects of adsorbent characteristics on its water adsorption performance were investigated using low-temperature oxygen plasma technology (LTOP) as a surface modification method. A series of activated carbon fiber (ACF)-based adsorbents was prepared to get further insight into the functions of water vapor adsorption behavior with textural property and surface chemistry. The result shows that LTOP treatment does not alter drastically the physical surface properties and simultaneously functionalize oxygen-containing functional groups (OFGs) especially carboxyl groups on the ACF surface when the treatment time and effective output voltage are 15 min and 8–9 kV, respectively. Meanwhile, the carbon atoms with unpaired electrons are found to be increased during the process of plasma treatment and used as active sites for chemical adsorption. Both OFGs and carbon atoms with unpaired electrons on the carbon surface play a vitally important role for water vapor adsorption. The surface functionalities and chemical adsorption may govern the adsorption–desorption behavior of water vapor at low relative humidity (RH less than 40%). Adsorption mechanism of water vapor on the carbon surface before and after LTOP treatment is proposed. After several adsorption and desorption cycles, the adsorption capacity of LTOP-treated ACFs is still higher than that of ACF-raw. Therefore, this technology may shed light on the potential application of LTOP-treated ACFs in harvesting water from air at low relative humidity.

Blue and near infrared luminescence degradation by electron beam irradiation in Y2O3:Tm3+ nanophosphors

Cathodoluminescence (CL) degradation measurements on Y2O3:Tm3+ nanoparticles were made to test for potential application as a blue phosphor in low-voltage field emission displays. The incorporation of Tm3+ into the Y3+ sites in the Y2O3 lattice was confirmed by x-ray photoelectron spectroscopy and CL spectra. The Y2O3:Tm3+ nanophosphor was investigated under vacuum and oxygen (O2) backfilled conditions in order to control surface chemical adsorption. The Auger electron spectroscopy (AES) and the CL data collection were performed simultaneously when the nanophosphor was bombarded with a beam of electrons with a 3 μA beam current and an accelerated voltage of 2 keV in both atmospheres. The Y2O3:Tm3+ nanophosphor displayed strong blue (457 nm) and relatively weak near infrared (812 nm) emissions. The CL intensity decreased as a function of electron dose in vacuum, while in the O2 backfilled pressure it only started to decrease after an electron dose of ∼250 C/cm2 after removal of C from the surface. The CL emission’s intensity increased at an initial electron dose in the O2 backfilled pressure due to the desorption of C from the surface. The removal of C and other surface impurities from the surface was ascribed to be due to electron stimulated surface chemical reactions. The AES and the thermoluminescence (TL) data suggested that an O deficient layer was formed on the surface. TL glow curves confirmed that the electron beam induced deep traps at activation energies of 1.28, 1.37, and 1.42 eV in the Y2O3:Tm3+ nanophosphor that was attributed to oxygen vacancies. Mechanisms, where O deficiency leads to an improvement in the CL intensity, were also discussed.

Aspirin Adsorption onto Activated Carbon Derived from Spent Tea Leaves: Statistical Optimization and Regeneration Study

Contamination of water sources by contaminants of emerging concerns, including pharmaceutical compounds, threatens the well-being of human who relies on the water sources. Development of cost-effective adsorbents for maximum removal of these contaminants is important to ensure clean and safe water access. This study demonstrates the reusability of activated carbon synthesized from spent tea leaves (STL-AC) for aspirin adsorption at optimized conditions. The maximum aspirin removal was 98.97% after optimization of process conditions using Response Surface Methodology. The adsorbent can be reused up to five cycles via solvent elution, with aspirin removal percentage above 85%. The repeated adsorption–desorption cycles affected the adsorbent textural properties, however the adsorbent surface chemistry was not affected by the regeneration. The aspirin adsorption proceeds via pore filling together with hydrogen bonding and π–π interaction between the aspirin molecules, however electrostatic repulsion between the deprotonated aspirin molecules and negatively charged STL-AC resulted in reduced removal percentage at high solution pH. This study signifies the superior property of STL-AC in adsorptive removal of aspirin, therefore the potential of such adsorbent in treatment of municipal wastewater, as well as hospital and pharmaceutical manufacturing effluents will be investigated.