Zeolite Materials Research Articles

Speciation-specific chromium bioaccumulation and detoxification in fish using hydrogel microencapsulated biogenic nanosilver and zeolite synergizing with biomarkers.

Grass carp intestinal waste-mediated biosynthesized nanosilver (AgNPs) was valorized using guaran and zeolite matrices, resulting in AgNPs-guaran, AgNPs-zeolite, and AgNPs-guaran -zeolite composites. The valorized products were examined using Environmental Scanning Electron Microscopy, Energy Dispersive X-ray analysis and X-ray Diffraction analysis to confirm uniform dispersion and entrapment of AgNPs within the matrixes. These valorized products were evaluated for their efficacy in detoxifying the ubiquitous and toxic hexavalent chromium (Cr6+) in aquatic environments, with Anabas testudineusexposed to 2mgl-1 of Cr6+ for 60days. Remarkable reduction of Cr6+ concentration to 0.86 ± 0.007mgl-1 was achieved with AgNPs-guaran-zeolite composite, indicating successful reclamation of contaminated water and food safety assurance. Consistency in results was further corroborated by minimal stress-related alterations in fish physiological parameters and integrated biomarker response within the experimental group treated with the AgNPs-guaran-zeolite composite. Despite observed chromium accumulation in fish tissues, evidence of physiological stability was apparent, potentially attributable to trivalent chromium accumulation, serving as an essential nutrient for the fish. Additionally, the challenge study involvingAnabas testudineus exposed to Aeromonas hydrophila exhibited the lowest cumulative mortality (11.11%) and highest survival rate (87.5%) within the same experimental group. The current study presents a novel approach encompassing the valorization of AgNPs for Cr6+ detoxification under neutral to alkaline pH conditions, offering a comprehensive framework for environmental remediation.

Enhanced dehydroaromatization of methane with methanol on Mo-ZSM-5/ZSM-11 intergrown zeolite materials

Methane dehydroaromatization (MDA) represents an appealing route for the direct utilization of abundant methane resources. Currently, the major challenge of MDA reaction lies in the rapid catalyst deactivation via coke formation, hindering large-scale industrialization of the process. Herein we report an enhanced conversion route of MDA in the presence of methanol on Mo-based zeolite materials. Compared to regular ZSM-5, ZSM-11, and their mechanically mixed counterparts, Mo embedded in ZSM-5/ZSM-11 intergrown matrix exhibits higher methane conversion (16.0%) and aromatics selectivity (62.5%) while limiting coke production to 12.1% under the co-feeding of methane and methanol (nCH4/nCH3OH = 30). If no methanol addition, coke selectivity is up to 45.1% in MDA reaction. Additionally, hydrogen enriched syngas (nH2/nCO = 6) was obtained as a co-product of the methane and methanol co-aromatization. NH3-adsorbed 1H MAS NMR, Co2+ titrated UV-vis and Raman spectroscopy characterizations reveal that a proper amount of Brönsted acid sites and the binuclear Mo anchored on the Al pairs at the intersection cavity may account for the superior reaction performance of the intergrown zeolites. A catalytic mechanism was also proposed via 13CH3OH isotopic labeling tracer and in-situ13C solid-state NMR studies. Methanol is first decomposed into CO/H2, while CO is hydrogenated to CH4 and converted into CO2 via the water-gas shift reaction. Alternatively, methanol is converted into CO/CO2 through formate intermediates. Subsequently, CO2 reduces coke deposition via the reverse Boudart reaction, which improves the catalytic performance.

Immobilization of 137Cs in NaY type zeolite matrices using various heat treatment methods

The accumulation of liquid radioactive waste presents a significant global challenge, necessitating effective strategies for safe management. This study investigates the immobilization of 137Cs radionuclides, a prominent component of liquid radioactive waste, in ceramic matrices based on 137Cs-saturated NaY Faujasite zeolite. Various thermal methods were employed, including cold pressing and sintering, cold pressing and sintering with microwave assistance, hot pressing, and spark plasma sintering, to enhance immobilization capabilities. Zeolite powder was saturated with 137Cs radionuclides using an adsorption technique with low-activity model liquid radioactive waste. In-situ XRD and dilatometry methods were used to study the thermal behavior during NaY Faujasite annealing. The influence of calcination temperature on lattice parameters and crystallite size was assessed. Immobilization effectiveness was evaluated through relative density, Vickers microhardness, compressive strength, and metal ion leaching kinetics. Mechanistic evaluation was performed using XRD and SEM-EDX studies. Results showed that spark plasma sintering exhibited the highest efficiency for immobilizing 137Cs radionuclides in NaY Faujasite matrices. This research contributes to liquid radioactive waste management by providing insights into the thermal behavior and enhanced immobilization capabilities of ceramic matrices.

Synthesis and Characterization of Silver-Modified Nanoporous Silica Materials for Enhanced Iodine Removal.

In aquatic environments, the presence of iodine species, including radioactive isotopes like 129I and I2, poses significant environmental and health concerns. Iodine can enter water resources from various sources, including nuclear accidents, medical procedures, and natural occurrences. To address this issue, the use of natural occurring nanoporous minerals, such as zeolitic materials, for iodine removal will be explored. This study focuses on the adsorption of iodine by silver-modified zeolites (13X-Ag, 5A-Ag, Chabazite-Ag, and Clinoptilolite-Ag) and evaluates their performance under different conditions. All materials were characterized using scanning electron microscopey (SEM), energy-dispersive X-ray spectroscopy (EDS), powdered X-ray diffraction (P-XRD), Fourier-transform infrared spectrometry (FTIR), and nitrogen adsorption studies. The results indicate that Chabazite-Ag exhibited the highest iodine adsorption capacity, with an impressive 769 mg/g, making it a viable option for iodine removal applications. 13X-Ag and 5A-Ag also demonstrated substantial adsorption capacities of 714 mg/g and 556 mg/g, respectively, though their behavior varied according to different models. In contrast, Clinoptilolite-Ag exhibited strong pH-dependent behavior, rendering it less suitable for neutral to slightly acidic conditions. Furthermore, this study explored the impact of ionic strength on iodine adsorption, revealing that Chabazite-Ag is efficient in low-salinity environments with an iodine adsorption capacity of 51.80 mg/g but less effective in saline conditions. 5A-Ag proved to be a versatile option for various water treatments, maintaining its iodine adsorption capacity across different salinity levels. In contrast, Clinoptilolite-Ag exhibited high sensitivity to ionic competition, virtually losing its iodine adsorption ability at a NaCl concentration of 0.1 M. Kinetic studies indicated that the pseudo-second-order model best describes the adsorption process, suggesting chemisorption mechanisms dominate iodine removal. Chabazite-Ag exhibited the highest initial adsorption rate with a k2 value of 0.002 mg g-1 h-1, emphasizing its superior adsorption capabilities. Chabazite and Clinoptilolite, naturally occurring minerals, provide eco-friendly solutions for iodine adsorption. Chabazite superior iodine removal highlights its value in critical applications and its potential for addressing pressing environmental challenges.

Efficacy of zeolites in radon adsorption: state of the art and development of an optimized approach

ABSTRACT Radon is a radioactive noble gas omnipresent in the environment, being part of the 238U and 232Th decay chains present in the Earth's crust. The gas can easily leak through the ground but also be present in natural construction materials and migrate into indoor places where it can be a carcinogen when inhaled. Studying the content and removal of indoor radon is crucial for the evaluation and mitigation of its radiological risks to public health. For more than 100 years, the removal by adsorption of the radon has been performed on activated charcoal. There is little progress in the field of radon adsorption at ambient conditions; the main progress is in the use of zeolite materials, having well-defined three-dimensional porous structures and radiation resistance. This study concerns a report on the state of the art of the application of zeolites in radon adsorption. Furthermore, an optimized approach for measuring the radon content in indoor environments and, consequently, its removal has been proposed. Adsorption systems based on zeolites have the potential to replace activated charcoal as a material of choice, allowing to facilitate the development of simple and compact radon adsorption systems.

Electrochemical Detection of Arsenic Using Eco-Friendly Zeolite-Graphite Composite Electrode

This paper presents an innovative and stable electrochemical sensor using zeolite and graphite for the reliable and accurate detection of arsenic(V). The zeolite materials were hydrothermally synthesized using coal fly ash and fumed silica by-products under specific environments (1.5 M NaOH, L/(Si/Al) ratio of 40, 120 °C, and 24 h), addressing environmental concerns related to wastes managment. The performance of the zeolite-graphite modified electrode (ZGME) was evaluated using voltammetric and impedance techniques at potentials between 1.2 V and −1.2 V (vs SCE) and a frequency range of 100 kHz to 10 mHz, respectively. The results showed that the incorporation of zeolite for the first time offered notable advantages, such as affordability, simplicity, and improved oxidation-reduction current and peak resolution for arsenic. The ZGME effectively detected As(V) under neutral conditions using a phosphate buffer solution, with a concentration range of 1 × 10−3 to 1 × 10−6 mol.l−1. The sensor achieved a detection limit of 3 μmol.l−1, a quantification limit of 5 μmol.l−1, a sensitivity of 0.28 μA/μM.cm2, and exhibited good reproducibility, opening up new potential for portable zeolite-based electrochemical sensors. Moreover, this research pioneers the use of zeolite as a graphite modifier.

Zeolite Synthesis from Natural Kaolin: The Effect of Metakaolin Heating and Transformation

In this study, the effect of kaolin heating and metakaolin transformation on zeolite synthesis was investigated. Two different metakaolin temperatures at the early stage of transformation were chosen in determining the lowest temperature that was capable of synthesizing the zeolite structure from natural kaolin. The synthesis of zeolite materials from the transformation of natural kaolin to metakoalin was conducted through the hydrothermal method. Natural kaolin obtained from Ipoh, Perak, was calcined at two different calcination temperatures of 600°C and 650°C. Metakaolin was obtained after 2 hours of exposure at 600°C and 650°C, respectively, with slightly different FTIR peaks of quartz at both temperatures. The incomplete metakaolin formation at a slightly lower temperature revealed the unsuccessful zeolite formation. At slightly higher calcination temperatures, the metakoalin peak obviously existed and led to the formation of the complete zeolite phase.This experiment also proved the importance of accurate calcination temperature in converting to zeolite synthesis. Furthermore, this current work also revealed that the complete transformation of metakoalin that can be conducted slightly lower temperature as compared to the common metakoalin phase will minimize energy consumption during the zeolite synthesis as well as the metakoalin transformation.

Purified Clinoptilolite-Tuff as an Efficient Sorbent for Food-Derived Peanut Allergens.

The avoidance of allergen intake is crucial for persons affected by peanut allergy; however, the cross-contamination of food is common and leads to unpredictable consequences after the consumption of supposedly "safe" food. The aim of the present study was to eliminate harmful traces of peanut allergens from food using purified clinoptilolite-tuff (PCT)-a specially processed zeolite material. Analyses were performed using a peanut ELISA and a Coomassie blue (Bradford) assay. Mimicking conditions of the human gastrointestinal tract demonstrated a higher efficacy of PCT in the intestine (pH 6.8) than in the stomach (pH 1.5). Adsorption rates were fast (<2 min) and indicated high capacities (23 µg and 40 µg per 1 mg of PCT at pH 1.5 and pH 6.8, respectively). Allergenically relevant peanut protein concentrations were sorbed in artificial fluids (32 µg/mL by 4 mg/mL of PCT at pH 1.5 and 80.8 µg/mL by 0.25 mg/mL of PCT at pH 6.8) when imitating a daily dose of 2 g of PCT in an average stomach volume of 500 mL. Experiments focusing on the bioavailability of peanut protein attached to PCT revealed sustained sorption at pH 1.5 and only minor desorption at pH 6.8. Accompanied by gluten, peanut proteins showed competing binding characteristics with PCT. This study therefore demonstrates the potential of PCT in binding relevant quantities of peanut allergens during the digestion of peanut-contaminated food.

Study on adsorption and purification materials for ethylene in cold storage

In view of the lack of systematic quantitative and comparative studies on the purification effect of ethylene adsorbent in cold storage, starting from the selection of purification materials, this paper analyzed the purification effect of different zeolite materials on ethylene through a small test chamber, and screened out the best zeolite adsorbents used in self-made purification device. Combined with characterization analysis, purification efficiency evaluation and adsorption capacity of zeolite material, the removal performance of ethylene was investigated. The results showed that the zeolite samples with rough and porous surface showed better adsorption performance for ethylene. The larger the specific surface area and total pore volume, the stronger the adsorption capacity to ethylene. In addition, the presence of Na elements and mesoporous increased the exchange capacity and pore volume, which also played a certain role in the ethylene adsorption process. Experimental result demonstrates that clean air volume (CADR) of ethylene is 232 m3/h, the ethylene removal rate at 30 min is 98.19%, and the purification energy efficiency is 1.39. At the same time, the adsorption capacity of the selected zeolite sample is 1380.5 μg/g by dynamic adsorption experiment, and the service life of the filter element of the self-made purification device is estimated to be 166 days. This study can provide a theoretical basis for ethylene purification in cold storage.

Impact of Cations and Framework on Trapdoor Behavior: A Study of Dynamic and In Situ Gas Analysis.

Due to their distinct and tailorable internal cavity structures, zeolites serve as promising materials for efficient and specific gas separations such as the separation of /CO2 from N2. A subset of zeolite materials exhibits trapdoor behavior which can be exploited for particularly challenging separations, such as the separation of hydrogen, deuterium, and tritium for the nuclear industry. This study systematically delves into the influence of the chabazite (CHA) and merlinoite (MER) zeolite frameworks combined with different door-keeping cations (K+, Rb+, and Cs+) on the trapdoor separation behavior under a variety of thermal and gas conditions. Both CHA and MER frameworks were synthesized from the same parent Y-zeolite and studied using in situ X-ray diffraction as a function of increasing temperatures under 1 bar H2 exposures. This resulted in distinct thermal responses, with merlinoite zeolites exhibiting expansion and chabazite zeolites showing contraction of the crystal structure. Simultaneous thermal analysis (STA) and gas sorption techniques further demonstrated how the size of trapdoor cations restricts access to the internal porosities of the zeolite frameworks. These findings highlight that both the zeolite frameworks and the associated trapdoor cations dictate the thermal response and gas sorption behavior. Frameworks determine the crystalline geometry, the maximum porosities, and displacement of the cation in gas sorption, while associated cations directly affect the blockage of the functional sites and the thermal behavior of the frameworks. This work contributes new insights into the efficient design of zeolites for gas separation applications and highlights the significant role of the trapdoor mechanism.

Predictive thermochemistry of Zeolitic materials using accessible practical procedures

Zeolites have wide application in industry, agriculture, medicine for ion exchange, for catalysis, and even for drug delivery so that it is important to understand their stability and synthesis. Although the standard thermochemical quantities (formula volume, enthalpies, entropies, and heat capacities) of zeolites are quite widely reported, there have been no general predictive procedures for the potentially vast numbers of possible examples of zeolites.We here consider some simple additive schemes for prediction of such properties. These demonstrate that zeolites behave in broad outline as standard ionic solids with dominant coulombic interactions. The Atom Sum method provides the necessary data for first thermochemical prediction with no need for inclusion of special group contributions.

Gaussian process regression with levy flight optimization: Advanced AR66 adsorption studies

The coal fly ash (CFA), which is the residue generated by coal-fired power plants, was converted into a valuable zeolite material known as zeolite P (ZNa-P) through thermal and acid pretreatments followed by microwave radiation. Various analytical techniques were utilized to analyze the resulting zeolite, including X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, BET analysis, and zeta potential measurement. The efficiency of ZNa-P in eliminating anionic dyes from aqueous solutions was exhibited by successfully removing acid red dye 66 (AR66) from a solution composed of water. To optimize the removal process, Central Composite Design (CCD) was applied to investigate the impact of four main parameters: solution pH, initial dye concentration, adsorbent mass, and contact time. The generated CCD database was modeled using Gaussian process regression (GPR) with the Lévy flight distribution (LFD) optimization algorithm. The GPR model was then used to determine optimal conditions for maximum AR66 absorption (3405.3 mg/g), with a pH of 2, initial dye concentration of 1000 mg/L, adsorbent mass of 0.2 g/L, and contact time of 11 minutes. Furthermore, the GPR model exhibited significantly lower error (32.58 mg/g) in predicting the experimental values compared to the CCD model (204.92 mg/g), highlighting the efficiency and superiority of the GPR model in this study.

High-efficiency lanthanum-modified zeolite adsorbents for phosphorus control and algal suppression: Preparation, characterization and mechanistic insights

The use of lanthanum (La)-based materials for phosphate removal from water has received increasing attention. However, challenges remain to enhance phosphate (P) sorption capacities and remove P at low concentrations. In this study, lanthanum modified zeolite materials loaded with different lanthanum types were synthesized by hydrothermal method. Based upon preliminary screening of synthesized La-modified zeolite materials in terms of phosphate sorption capacity and La content, lanthanum chloride-modified zeolite (LZ) is chosen for further study. Specifically, for these materials, phosphate sorption kinetics and isotherm behavior, and solution matrix effects (solution pH, and ionic strength) are reported. The developed LZ has a high sorption capacity of 124.38 mg/g, which exceeds that of most La-based adsorbents currently available. P uptake by LZ was pH-dependent with the highest sorption capacities observed over a pH range of 3 ∼ 9. The presence of coexisting ions (Cl-, SO42-, HCO3–) does not significantly affect the adsorption capacity of LZ. In a real treated wastewater effluent with phosphate concentration of 1.92 mg/L and 0.155 mg/L, 0.1 g/L and 0.01 g/L of LZ efficiently reduced the phosphate concentration to below 0.01 mg P/L. Electrostatic attraction and inner-sphere complexation were identified as the sorption mechanisms of phosphate by LZ. The acute toxicity test confirms that the addition of LZ has no acute toxicity effect on aquatic organisms. However, LZ shows indirect and direct inhibitory effects on algae growth, which is beneficial for the control of eutrophic water. Moreover, the exhausted LZ can be easily regenerated with over 70 % adsorption capacity remained during five recycles. Overall, LZ shows great application potential, and this work provides new insights into the molecular-level mechanism of phosphate sequestration by LZ.

Measuring flow rate and purity in portable oxygen concentrators

For people with respiratory disorders who need additional oxygen therapy, oxygen concentrators are vital medical equipment. By concentrating oxygen from the ambient air, they function to give the user a greater flow of oxygen-enriched air. The application of lithium zeolite for oxygen concentration in POCs is the most intense part of this work. One kind of zeolite material that may selectively absorb nitrogen from the air to increase oxygen concentration is lithium zeolite. The capacity, effectiveness, and dependability of a POC fitted with lithium zeolite are all examined in this study, along with its overall performance. The findings show that lithium zeolite, which has benefits including high oxygen purity and low energy consumption, is a potential material for use in POCs. The results of this study aid in the creation of POCs for oxygen therapy that are more effective and efficient. This study suggests utilizing an Arduino microcontroller and an HX710B air pressure sensor to measure the oxygen flow rate in a POC. The POC’s oxygen flow channel incorporates the HX710B sensor to monitor pressure variations, which the Arduino uses to translate into flow rate readings. To verify the accuracy and dependability of the system, its performance is assessed under different flow rate scenarios. Lithium zeolites are well-known for having a high selectivity for nitrogen adsorption, which can enhance the concentrator’s oxygen separation process’s effectiveness. Lithium-zeolite-based oxygen concentrators may have a lower environmental effect than standard concentrators.

A Zeolitic Octahedral Metal Oxide with Ultrahigh Porosity for High‐temperature and High‐humidity Alkyne/Alkene Separation

AbstractZeolitic octahedral metal oxide is a newly synthesized all‐inorganic zeolitic material and has been used for adsorption, separation, and catalysis. Herein, a new zeolitic octahedral metal oxide was synthesized and characterized. The porous framework was established through the assembly of [P2Mo13O50] clusters with PO4 linkers. Guest molecules occupied the framework, which could be removed through heat treatment, thereby opening the micropores. The pore characteristics were controlled by the cations within the micropore, enabling the adjustment of the interactions with alkynes and alkenes. This resulted in good separation performance of ethylene/acetylene and propylene/propyne even under high temperature and humidity conditions. The high stability of the material enabled the efficient recovery and reuse without discernible loss in the separation performance. Due to the relatively weak interaction between the adsorbed alkyne and the framework, the adsorbent facilitated the recovery of a highly pure alkyne. This feature enhances the practical applicability of the material in various industrial processes.

A Zeolitic Octahedral Metal Oxide with Ultrahigh Porosity for High-temperature and High-humidity Alkyne/Alkene Separation.

Zeolitic octahedral metal oxide is a newly synthesized all-inorganic zeolitic material and has been used for adsorption, separation, and catalysis. Herein, a new zeolitic octahedral metal oxide was synthesized and characterized. The porous framework was established through the assembly of [P2Mo13O50] clusters with PO4 linkers. Guest molecules occupied the framework, which could be removed through heat treatment, thereby opening the micropores. The pore characteristics were controlled by the cations within the micropore, enabling the adjustment of the interactions with alkynes and alkenes. This resulted in good separation performance of ethylene/acetylene and propylene/propyne even under high temperature and humidity conditions. The high stability of the material enabled the efficient recovery and reuse without discernible loss in the separation performance. Due to the relatively weak interaction between the adsorbed alkyne and the framework, the adsorbent facilitated the recovery of a highly pure alkyne. This feature enhances the practical applicability of the material in various industrial processes.

Recycling of fly ash to synthesize zeolites for efficient removal of dioxins

The large amount of fly ash (FA) produced by coal-fired power plants places tremendous pressure on the environment. Meanwhile, toxic dioxins emitted from municipal solid waste incineration plants are of great concern. To address these challenges, a win-win approach was proposed to re-utilize FA for synthesis of zeolite materials for dioxins adsorption. The results indicate that the Si/Al molar ratio in the liquid-phase precursor significantly influences the distribution of Si-Al 4-membered rings (Si/Al=1) and Si-Al 4-membered rings (Si/Al=3) in the system. These units are key secondary structures of the zeolite skeleton, determining the proportions of A-type and X-type zeolites in the product. With the increasing Si/Al molar ratio of precursor, the specific surface area and Si/Al molar ratio of zeolites derived from fly ash (ZFA) both increased, while they played a positive and negative role in dioxins adsorption, respectively. The adsorption of dioxins by ZFA peaked at a Si/Al molar ratio of precursor of 1.5, reaching 4.13×105 pg I-TEF/g, surpassing activated carbon by 1.46 times. This study not only elucidates the mechanism of Si/Al molar ratio of precursor on crystalline transformation of ZFA, but also confirms the potential of ZFA in dioxins adsorption.

Natural mineral raw materials as granular filtering materials in industrial and waste water treatment

Analysis of currently existing methods of natural and waste water treatment from heavy metals has shown that one of the most promising is the sorption method using natural inorganic materials as sorbents: zeolite, diatomite, and vermiculite. The relevance of the topic is dictated by the need to develop an original technology of wastewater treatment and water treatment, which allows constant monitoring of the level of pollution of natural waters by industrial wastewater from metallurgical enterprises. The proposed methods of sorbent modification create a basis for studying the structure, porosity, and sorption capabilities of the mentioned natural materials. All three minerals: zeolite, diatomite, and vermiculite belong to highly porous, structured materials, promising for use as stable sorption systems in water treatment and water purification. The influence of physical and chemical characteristics of natural sorbents and the application of new promising environmentally safe materials and reagents for water treatment are considered. The sorption of copper ions on natural zeolite material before and after its modification by hydrothermal method was investigated. The activity of sorbents was estimated by the value of sorption capacity, i.e. the amount of heavy metal ions absorbed by a unit mass of sorbent based on zeolite and its modified form.

Synthesis of a TiO2/zeolite composite: Evaluation of adsorption-photodegradation synergy for the removal of Malachite Green

Preparing by a simple method a versatile and sustainable material that can simultaneously perform effectively as an adsorbent/photocatalyst is a real challenge in wastewater treatment technology. In this work, a composite with 10% (wt%) TiO2 nanoparticles supported on zeolite (TiO2-Zeo) was synthesized by a facile-solid-state dispersion method, and characterized for their physicochemical, phase structure, microstructure, and optical properties. Characterization findings, showed that, for TiO2-Zeo catalyst, the zeolitic matrix preserved its initial structure without any alteration, while its gap energy of 3.23 eV was similar to that of the starting TiO2 material, showing that TiO2 nanoparticles were simply deposited on the surface of the zeolite support. TiO2-Zeo photocatalyst, as well as commercial TiO2 nanoparticles, tested here as a photocatalyst model in view of comparison, were used for the removal of Malachite Green dye (MG) from aqueous solution. The adsorption and photodegradation potential of the catalysts was evaluated under the same operating conditions. It was found that the adsorption kinetics for the two materials were relatively slow, and the pseudo-first-order model can describe accurately the adsorption kinetics data. The equilibrium states were reached after 140 min and 150 min for MG/TiO2-Zeo and MG/TiO2 systems. At 0.5 g.L-1 dose of TiO2-Zeo, the adsorption capacity of MG at equilibrium, and the removal efficiency obtained with 25 mg.L-1 and 35 mg.L-1 were 41.2 mg.g-1 (82.3%), and 46.9 mg.g-1 (65.6%), respectively. Whereas, after 240 min UV irradiation, the obtained values in synergistic adsorption-photodegradation dye removal were superior, namely 47.4 mg.g-1 (92.7%) and 63.6 mg.g-1 (90.2%), respectively. On the other hand, within the range of operating conditions considered, the overall kinetic rate of synergistic adsorption-photodegradation was also simulated using the modified Elovich heterogeneous kinetic model in the two following scenarios: for strong and weak adsorption. Based on the goodness-of-fit criteria values obtained with the two used catalysts, the model appeared globally very consistent with kinetic data in both cases, with a perfect agreement in the strong adsorption case.

Advancing self-cleaning performance in metakaolin-based geopolymers through in-situ zeolite formation and TiO2 integration

The deterioration of self-cleaning properties of cementitious materials upon hydration was addressed by in-situ zeolite formation within metakaolin-based geopolymers. Pastes with varied in-situ zeolite content were formulated by adjusting the Si/Al ratio of initial raw materials and curing temperatures. The impact of in-situ zeolite formation on self-cleaning performance was systematically investigated through phase composition, optical property and microstructure analyses. Zeolite A formation notably enhances self-cleaning performance, despite contributing to higher band energy and lower Urbach energy. The increases in crystalline zeolite amount and matrix porosity enhances mass transfer capacity. The open pore structure of zeolite facilitates the formation of connective channels during particle growth, mitigating the “sheltering” effect of the surrounding media for photocatalysts and ensuring improved self-cleaning performance upon hydration. This study summarizes the synthesis conditions for zeolite A, providing mechanistic insights into in-situ zeolite formation in metakaolin-based geopolymers and emphasizes its promising potential for optimizing self-cleaning properties in cementitious materials.