Abstract The brick production industry faces increasing environmental pressure due to high energy demands during firing, necessitating the optimization of firing conditions. This study investigates an eco-friendly stepped firing process as a sustainable alternative to conventional direct heat treatment using clayey raw materials from the Ouled Mansour area, north-east Morocco. To evaluate this approach, raw materials were characterized using X-ray diffraction, X-ray fluorescence, infrared spectroscopy, simultaneous thermal analysis, Atterberg limits and particle-size distribution analysis. Brick specimens were then prepared and fired under both conventional and stepped heating processes. Their thermophysical properties (thermal conductivity, thermal diffusivity, porosity, water absorption and density) and compressive strength were assessed. Non-destructive tests (ultrasonic pulse velocity and Schmidt hammer tests) together with mineralogical and microstructural analyses were also performed. The stepped firing process reduces porosity and defects, thereby increasing the ultrasonic pulse velocity from 3197 to 3508 m s –1 and improving compressive strength by up to 21%. Thermal conductivity and density slightly increase, from 0.57 to 0.58 W mK –1 and from 1.60 to 1.62 g cm –3 at 770°C, respectively. The proposed eco-friendly firing process enhances the physico-mechanical performance of bricks while supporting their energy-efficient production, with potential reductions in energy consumption during both manufacturing and the building service life.
Abstract Engineering muck (EM) is an underutilized construction waste rich in clay minerals. The mechanical properties, composition, microstructures and reaction mechanisms of various EM-based geopolymers produced via acid or alkali activation are comprehensively compared and discussed in this study. The results indicate that EM mainly contains clay minerals (kaolinite, halloysite and dioctahedral mica), feldspar and quartz. The geopolymerization reactivity of EM was improved following crushing and calcination pretreatments, which destroyed the microstructure of the clay minerals and formed a reactive amorphous phase. Acid activation of calcined EM (EM 700°C ) resulted in greater geopolymerization reactivity than alkali activation. The highest 7 and 28 day compressive strengths of phosphoric acid-activated EM-based geopolymers reached 27.31 and 24.37 MPa, respectively, under a water/binder mass ratio of 0.7 and an Al/P molar ratio of 0.9. Comparatively, the maximum 7 and 28 day compressive strengths of alkali-activated EM-based geopolymers were only 7.82 and 11.66 MPa, respectively, under a water/binder mass ratio of 0.6 and a SiO 2 /Na 2 O molar ratio of 1.75. For phosphoric acid activation, reactive Al 3+ mainly from calcined clay (e.g. metakaolinite) in EM 700°C geopolymerized with PO 4 3– and silica, forming phosphate-containing phases and amorphous silico-aluminophosphate (SAP; Si–O–Al–O–P) gels. In contrast, reactive SiO 2 and Al 2 O 3 from EM 700°C participated in the geopolymerization process in alkaline solution, forming sodium aluminosilicate hydrate (N–A–S–H) gels and the byproduct faujasite. The geopolymerization reactivity of EM 700°C and the resulting composition variations in various solutions contributed to the differences in the compressive strengths of EM-based geopolymers. This study provides a theoretical basis for preparing acid/alkali-activated geopolymers from EM.
Abstract Natural zeolites modified with iron(II) ions or iron(III) phases represent two promising approaches for treating hexavalent chromium contamination in water due to their reduction and adsorption capacities, respectively. However, comprehensive comparative analysis of their efficiency remains limited. Fe(II)-modified zeolites can reduce Cr(VI) to the less toxic and insoluble Cr(III) form, while Fe(III)-modified zeolites primarily remove Cr(VI) through surface adsorption. This study evaluates the effectiveness of Fe(II)- and Fe(III)-modified zeolites using synthetic Cr solutions and real contaminated surface water. The materials were characterized via X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray fluorescence spectroscopy to assess their chemical, structural and morphological changes before and after chromium sorption. Batch and column tests determined Cr(VI) removal capacity, while Cr isotopes were used to track reduction reactions. The Fe(II) enrichment via cation exchange was highly effective. The Fe(II)-modified zeolite demonstrated a greater capacity for Cr(VI) removal from contaminated solutions, primarily through a reduction mechanism that converted Cr(VI) to Cr(III), as was confirmed by isotopic analysis. Its performance improved under higher-salinity conditions. However, it required prolonged contact time with the contaminant to achieve optimal efficiency. The Fe(III)-modified zeolite exhibited a heterogeneous distribution of iron oxide/hydroxide phases on its surface. This material showed some favourable characteristics in batch and column tests, including a notably faster Cr removal rate due to direct Cr(VI) sorption. However, it could only perform well when no other competitive ions were present in the solution, severely impacting its application in complex, real matrices.
Abstract Claystones and related sedimentary lithologies are considered as potential host rocks for the storage of high-level radioactive waste. The properties of claystones, which govern their barrier performance, can vary significantly between sites and formations. This study summarizes relevant barrier properties, with a particular emphasis on those dependent on burial history and maximum rock temperatures. Given the large number of properties influencing barrier quality, ranking them by relative importance is necessary. The predictable, non-linear behaviour of certain characteristics with geological burial depth allows for a substantial reduction in the number of properties requiring determination. Based on a set of representative repository-relevant rock lithologies, a case study comparison of potential claystone host rocks is presented. Hydraulic conductivity was assumed to be the most critical barrier property, with optimal values in rocks that reached peak diagenesis at burial depths exceeding 2000 m. To further distinguish claystone types and related lithologies in terms of barrier suitability, either cation-exchange capacity, reflecting the content of smectitic layers, or maximum temperature of palaeoburial heating ( T maxgeo ) can be used as an example. Pore-size distribution, correlating with the average particle distance, was particularly suited to estimating maximum burial depth, as it is less affected by thermal anomalies, pore fluid composition or cementation effects. Overall, combining key barrier properties with burial depth-dependent behaviour enables efficient assessment and comparison of claystone formations for deep high-level radioactive waste disposal. A quantitative comparison of various claystones, however, requires establishing a reactive solute transport model that simulates radionuclide release fluxes at specific timescales.
Abstract The structure of stacking faults in nacrite, a polytype of kaolin-group minerals, was revealed by atomic-resolution imaging using aberration-corrected scanning transmission electron microscopy, particularly by optimum bright-field imaging with a segmented annular detector, which can achieve a sufficient signal-to-noise ratio even at a very low electron dose. The results unambiguously demonstrated that nacrite, which belongs to polytypic Group D of 1:1 phyllosilicates, contains the stacking sequence of Group A as a stacking fault. This result suggests that the stacking sequences of different polytypic groups can coexist in dioctahedral 1:1 phyllosilicates, as well as in trioctahedral ones. Furthermore, the atomic-resolution images of nacrite showed weak contrasts at specific oxygen columns, suggesting partial dehydroxylation in nacrite induced by electron irradiation during imaging or focused ion beam processing.
Abstract Multifunctional coatings represent the most widely used strategy for extending the service life of metallic materials in harsh environments. However, coating performance is determined by the designed functional fillers, or the micro/nano-containers. Attapulgite (ATP) has attracted increasing attention in multifunctional coating systems because it can simultaneously improve barrier performance, act as a micro/nano-container for active agents, form surface micro- and nanostructures and regulate interfacial properties. These features enable its broad use in superhydrophobic, anti-corrosion, anti-bacterial/anti-fouling, self-cleaning/anti-smudge and anti-icing coatings. This review provides a comprehensive overview of recent progress in ATP-based multifunctional protective coatings. It examines the main pretreatment strategies for ATP, including thermal treatment, acid/alkali activation, hydrothermal treatment and solvothermal treatment, together with their influence on channel characteristics, surface activity, dispersibility and matrix compatibility. The diverse roles of ATP in coating systems are further discussed, ranging from barrier-phase reinforcement and micro/nano-container construction to roughness generation and interfacial functional regulation, as well as the corresponding protective mechanisms. By integrating the discussion of passive barrier enhancement and active functional protection, this review offers a unified perspective on the design of ATP-based multifunctional coatings. In addition, current challenges and future research directions are briefly outlined to promote the practical development of high-performance ATP-enabled protective coatings.
Abstract The significant threat posed by harmful microorganisms to human health and environmental sanitation has garnered considerable attention. Sepiolite, with its natural nanofibre structure, excellent physicochemical properties and good biocompatibility, shows great potential for antimicrobial applications in healthy living environments. In this study, magnesium oxide nanocrystal/sepiolite composites (MgO/sepiolite) were synthesized via an acid leaching–hydrothermal combined method using sepiolite without the addition of external magnesium salts, and their antimicrobial performance for bacteria and fungi was investigated. As both a magnesium source and carrier material, sepiolite effectively improved the dispersion of MgO nanoparticles by utilizing its large specific surface area, facilitating the formation of a greater quantity of smaller-sized MgO nanoparticles and abundant oxygen vacancies. The resulting MgO/sepiolite composites retained the fibre morphology of sepiolite, with the MgO nanoparticles uniformly dispersed on the fibre surface and with particle sizes in the range of 1.0–2.5 nm. The synergistic effects of these advantages of the MgO/sepiolite composite contributed to improved antimicrobial performance, leading to 99.99% antibacterial rates against Escherichia coli and Staphylococcus aureus , and a fungal growth grade of 0 against mixed fungi. Analyses of the pH value changes in the bacterial solution, Mg 2+ release, free radical concertation and Fourier-transform infrared spectra data revealed that the excellent antimicrobial performance is primarily attributable to oxygen vacancy-mediated reactive oxygen species damage. Additionally, the release of Mg 2+ , pH adjustment and contact killing synergistically improved the oxygen vacancy-mediated damage, thus contributing to the antibacterial performance. This study is expected to provide valuable insights into the design and development of novel clay-based antimicrobial function materials, particularly with respect to synthesis methodology and the elucidation of antimicrobial mechanisms.
Abstract The reduction of volatile organic compounds (VOCs), especially the oxidation of highly toxic and chemically resistant toluene, remains a challenge in environmental catalysis. In this research, a porous TiO 2 /SiO 2 support was initially fabricated through titanium pillaring of montmorillonite and then calcined and acid-leached as an efficient platform for Pt nanoparticle immobilization to yield Pt–TiO 2 /SiO 2 . The experimental data showed that the catalyst loaded with 0.37 wt.% Pt (0.37Pt–TiO 2 /SiO 2 ) exhibits superior toluene oxidation performance, reaching a T 90 of 190°C. Moreover, the catalyst exhibited remarkable water resistance, maintaining high efficiency even in the presence of 10% water vapour and outstanding long-term stability, with no substantial deactivation after 48 h of continuous operation. The performance improvement is explained by the high dispersion of Pt nanoparticles on the support and the metal–support interaction between Pt and TiO 2 , characterized by electron transfer from TiO 2 to Pt. This interaction facilitates the adsorption and activation of reactant molecules. In situ diffuse reflectance Fourier-transform infrared spectroscopy explained the catalytic mechanism: toluene is sequentially transformed into benzyl alcohol, benzaldehyde and benzoate intermediates, which are subsequently converted to maleic anhydride by opening the ring and eventually mineralized into CO 2 and H 2 O. This work developed a high-performance, durable catalyst using cost-effective and abundant natural minerals, offering promising prospects for practical abatement of industrial VOCs.
Rapid and efficient haemostasis is key to controlling bleeding and reducing mortality, and so it is necessary to design high-performance haemostatic materials. Here, haemostatic gauze composites were facilely prepared based on dopamine polymerization modification of gauze and simultaneous impregnation loading of mixed-dimensional palygorskite clay (MDPal). The haemostatic performance of gauze composites was systematically evaluated in comparison with a commercially available gauze impregnated with kaolin. The results confirmed that no obvious changes were observed regarding the water vapour transmittance and water absorption of the gauze after coating with polydopamine and MDPal. Blood coagulation studies indicated that the optimal gauze composites prepared with 200 mg of dopamine after reaction for 6.5 h presented superior haemostatic properties according to the in vitro blood-clotting index, the coagulation kinetics of platelet-poor plasma coagulation, erythrocyte adhesion behaviour and thrombus formation. The haemorrhage effects on rat liver bleeding suggested that the blood losses with the gauze composites were 8.52% and 29.45% less than that of the blank group. In addition, the coagulation time decreased by 38.12% compared with the blank group. Furthermore, the gauze composites exhibited good biocompatibility as evaluated by haemolysis rate and cytotoxicity assays. Thus, the obtained gauze composites can serve as promising candidates for rapid wound haemostasis.
Abstract Palygorskite (Pal) is a layered-chain clay mineral characterized by unique one-dimensional nanorod crystals, regular nanochannels and abundant surface active groups. Since the discovery of Pal’s presence in China in 1976, Chinese scientists have resolved the key bottleneck of efficient the disaggregation of the rod crystal bundles restricting its high-value utilization and achieved a fundamental transformation of Pal from a traditional raw mineral material to an advanced functional nanomaterial. The applications of Pal in China have expanded into diverse fields, including energy materials, antibacterial agents, catalysts, tissue engineering scaffolds, hydrogen storage materials, membrane separation materials, functional coatings and pigments, among others. In the case of naturally abundant mixed-dimensional Pal clays with complex mineral compositions, full-mineral synchronous utilization technology has been developed for the fabrication of functional materials based on the differences and complementarities in the structures and properties of the coexisting minerals. This article reviews the significant progress made by Chinese researchers in transforming nanostructured Pal into advanced functional materials, highlighting representative cases in green preparation and sustainable applications. Finally, future key research directions are proposed to promote the efficient and sustainable utilization of Pal resources, aligning with the disciplinary frontier of mineral materialization.
Converting CO2 into value-added fuels via photocatalysis represents a promising strategy to address the energy crisis and global climate challenges. The core of the matter lies in constructing an optimal photocatalytic system featuring broadband light utilization, high charge separation efficiency and abundant surface-active centres. To overcome obstacles including high cost, complex processes and poor environmental compatibility of synthetic photocatalysts, this study constructs kaolinite/pyrite (KL/Py) composite photocatalysts via a green mechanical ball milling method based on natural mineral symbiosis characteristics, using the abundant 1:1 layered clay mineral KL and the narrow-bandgap mineral Py as raw materials. Although the KL and Py used in this work are obtained from different commercial sources, their typical coexistence in sedimentary deposits inspires the design of this composite. By adjusting the composite mass ratio, the obtained composite exhibits the best photocatalytic activity, and its CO yield can reach up to 89.5 mu mol g(-1) h(-1), which is 2.3 times higher than that of Py alone. The synergistic interaction between KL and Py markedly improves the efficiency of charge transfer at the interface and inhibits the recombination of photogenerated carriers. In addition, the hydroxyl-enriched surface of KL serves as an active centre for CO2 uptake and hole capture. This composite photocatalyst demonstrates outstanding and durable performance in photocatalytic CO2 conversion and offers a novel theoretical foundation and an eco-friendly synthesis route for the value-added application of clay minerals and the development of natural mineral-based photocatalysts.
Abstract The 14 elements from La to Lu (except the unstable Pm) form a group with similar chemical characteristics provided by their electronic configurations. Widespread, albeit in low abundance (hence their original description as ‘rare’), they were soon viewed as an opportunity to trace rock origins and geological processes. In addition to this scientific use, their technological applications have increased over the decades, which have multiplied in the present electronic age. Their exponential growth in demand and limited abundance have transformed them into strategic resources. Characteristic of clay minerals, which take centre stage in so many industrial applications and scientific issues, they have been discovered to be involved in this story as important commercial rare earth element ( REE ) deposits. This review describes how phyllosilicates bind REE , how environmental conditions modify REE contents in phyllosilicates and how such interactions can be used to trace both original rocks and the nature of modifying geological processes. Phyllosilicates bind REE strongly and concentrate them as adsorbed species in inner and outer poly-coordination complexes. This mode of binding controls the capacity for REE retention by phyllosilicates in conjunction with the physicochemical conditions of environmental fluids (salinity, pH, temperature, ligands, Eh) and fluid:rock ratios to determine the contribution of clay minerals to bulk REE signatures and their modifications in geological processes (soil formation, clay mineral precipitation from fluids, alteration, diagenesis, ore formation, transport).
Abstract The influence of exchangeable alkali cations on glucose uptake, interlayer reorganization and ionic transport was investigated in homoionic Wyoming montmorillonite exchanged with the complete alkali series (Li + , Na + , K + , Rb + and Cs + ). Glucose adsorption was rapid during the initial stage and reached equilibrium after ∼6 h. Under the investigated conditions, the equilibrium uptake was highest for the Li- and Cs-exchanged forms, whereas the Na-exchanged form showed the lowest adsorption amount. X-ray diffraction, differential thermal analysis and Fourier-transform infrared spectroscopy collectively support partial accommodation of glucose within the interlayer region without major disruption of the aluminosilicate framework, although the magnitude of the structural response depended strongly on the exchangeable cation. The largest basal expansion was observed for the Li- and Na-exchanged forms, showing that interlayer opening does not directly parallel adsorption capacity across the alkali series. Broadband impedance spectroscopy further indicates thermally activated ionic transport and a marked cation dependence of both direct current (DC) conductivity and activation energy after glucose loading. In particular, glucose adsorption altered the conduction environment more strongly in the Li- and Na-exchanged systems than in the K-, Rb- and Cs-exchanged forms under the same thermal conditioning. Taken together, the results suggest that glucose uptake, interlayer expansion and ionic transport are governed by coupled effects involving cation hydration, interlayer accessibility and local structural organization rather than by a single cation property alone. This comparative dataset provides a basis for understanding how exchangeable cations regulate saccharide–clay interactions in montmorillonite.
