In sedimentary environments or clay-rich rocks, clay minerals are usually combined with organic matter; however, little research has focused on the effects of combinations of organic matter and clay minerals on the thermal degradation of organics and on subsequent hydrocarbon generation. In this study, the long-chain fatty acid octadecanoic acid (OA) and its derivative octadecy trimethyl ammonium bromide (OTAB) were selected as model organics. The organics were prepared for clay–organic associations with Na-based montmorillonite (Mt(Na)). The thermal decomposition behaviors of these associations were studied via thermogravimetric (TG/DTG) analysis. In the presence of Mt(Na), OA decomposed at 275.2 °C, decomposing sooner than pure OA. The thermal decomposition behavior of OTAB is nearly consistent with that of pure OTAB, but for interlayer OTAB, the decomposition temperature increased to higher than 300 °C. The results indicate that Mt(Na) plays a dual role in the thermal decomposition of fatty acid. Mt(Na) may accelerate the thermal decomposition of OA, and inherent solid acidity levels may be the key factor. In addition, the interlayer structure of Mt(Na) can increase the thermal stability of OA and OTAB. The above results further demonstrate that the thermal decomposition behavior of a given organic material may also depend on its structure and composition. In the presence of Mt(Na), organics with amino and amine structures are more stable than those with carboxyl groups.

•Five main stages in sol-gel growth of imogolite were outlined.•Morphological, structural and textural changes of imogolite in each stage were characterized in detail.•A sphere/tube transition occurred in formation of proto-imogolite.•The very initial spherical/tubular closed ILS were observed by AFM.Imogolite (Imo) was prepared via a sol-gel method. The time-dependent changes in its morphology, structure and texture during the whole synthesis process (from amorphous precursors to the final products through nanoscale intermediates) were monitored by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) and N2 physisorption. The results showed that a shape transition from a spherical open imogolite local structure (ImoLS) to a tubular open ImoLS occurred in the process of proto-imogolite (proto-Imo) formation. Based on the overall structure of the obtained solid products and the occurring main reactions, Imo synthesis process was described in five steps: i) formation of amorphous precursors by hydrolysis and condensation of Al and Si; ii) formation of proto-Imo with an open ImoLS at the expense of the amorphous precursors; iii) open ImoLS dominates; it grows and assembles into the first closed ImoLS (tubes and spheres); iv) closed ImoLS dominates and continues to form (mainly tubes) at the expense of open ImoLS; and v) no more open ImoLS; further growth of already-formed Imo via oriented aggregation. These findings provide new insights into the formation mechanism and structure of proto-Imo and Imo, which helps to clarify the Imo synthesis procedure.

•Different benzene adsorption behaviors and related mechanisms of montmorillonite, kaolinite and halloysite were studied.•Benzene adsorption of swelling clay minerals is influenced by not only the SSA but also the interlayer microporosity.•Benzene adsorption of non-expandable clay minerals is mainly affected by surface adsorption that is determined by the SSA.Montmorillonite (Mt), kaolinite (Kaol) and halloysite (Hal) are commonly investigated porous clay minerals, but their performance for the adsorption of volatile organic compounds (VOC) was rarely studied. In this work, the dynamic adsorption of benzene, as a model VOC, on Mt, Kaol and Hal was investigated. The effect of the microstructures of the above-mentioned clay minerals on benzene adsorption were explored by comparing the benzene adsorption of the different derivates of these clay minerals, which were obtained by adjusting the interlayer space and the porosity of the clay minerals through heating treatment. Calcium-based montmorillonite (Ca2 +-Mt) heated at 120 °C exhibited higher benzene adsorption capacity (141.2 mg/g) than sodium-based montmorillonite (Na+-Mt) heated at 120 °C (87.1 mg/g), because the interlayer distance of Ca2 +-Mt was sufficiently large to accommodate the adsorption of benzene. However, for calcined Ca2 +-Mt and Na+-Mt, the collapse of their interlayer space resulted in that the interlayer micropores no longer existed and reduced benzene adsorption. Kaol exhibited the lowest benzene adsorption capacity (56.7 mg/g) among the studied clay minerals because its interlayer space was not available for adsorption and because its specific surface area (SSA) was relatively small. As a polymorph of Kaol but with a tubular morphology, Hal showed a higher benzene adsorption capacity than Kaol owing to its larger SSA. In particular, heating at 120 °C resulted in the increase of the benzene adsorption of Hal, which was ascribed to the exposure of the adsorption sites initially occupied by water molecules. These results demonstrate that the benzene adsorption capacity of the above-mentioned clay minerals was not only highly related to their SSA but also strongly affected by their porosity features.

•Montmorillonite exhibits either pyrolysis-promoting or pyrolysis-inhibiting effect.•Brønsted acid sites promote hydrocarbons cracking through a carbocation mechanism.•Lewis acid sites in Mt promote the decarboxylation of OM containing carboxyl groups.•The interlayer space magnifies pyrolysis-promoting or pyrolysis-inhibiting effect.The stability and persistence of organic matter (OM) in source rocks are of great significance for hydrocarbon generation and the global carbon cycle. Clay-OM associations commonly occur in sedimentation and diagenesis processes and can influence the pyrolytic behaviors of OM. In this study, clay-OM complexes, i.e., interlayer clay-OM complexes and clay-OM mixture, were prepared and exposed to high-pressure pyrolysis conditions in confined gold capsule reactors to assess variations in OM pyrolysis products in the presence of clay minerals. Three model organic compounds, octadecanoic acid (OA), octadecy trimethyl ammonium bromide (OTAB), and octadecylamine (ODA), were employed and montmorillonite (Mt) was selected as the representative clay mineral. The solid acidity of Mt plays a key role in affecting the amount and composition of the pyrolysis gases generated by the clay-OM complexes. The Brønsted acid sites significantly promote the cracking of hydrocarbons through a carbocation mechanism and the isomerization of normal hydrocarbons. The Lewis acid sites are primarily involved in the decarboxylation reaction during pyrolysis and are responsible for CO2 generation. Mt exhibits either a catalysis effect or pyrolysis-inhibiting during pyrolysis of a given OM depending on the nature of the model organic compound and the nature of the clay-OM complexation. The amounts of C1–5 hydrocarbons and CO2 that are released from the Mt-OA and Mt-ODA complexes were higher than those of the parent OA and ODA, respectively, indicating a catalysis effect of Mt. In contrast, the amount of C1–5 hydrocarbons produced from the pyrolysis of Mt-OTAB complexes was lower than that of OTAB, which we attribute to an inhibiting effect of Mt. This pyrolysis-inhibiting effect works through the Hoffmann elimination that is promoted by the catalysis of the Brønsted acid sites of Mt, therefore releasing smaller amounts of gas hydrocarbons than the nucleophilic reaction that is induced by the halide ions in OTAB. In particular, the interlayer space of Mt acts as an ‘amplifier’ that magnifies the above-mentioned catalysis or pyrolysis-inhibiting effect, due to the greater number of Brønsted acid sites with high acidity in the interlayer space. These findings are potentially important for understanding the storage and transfer mechanisms of natural OM in sedimentation and diagenesis processes.

The structural incorporation of aluminium (Al) into diatomite is investigated by preparing several Al–diatomite composites by loading an Al precursor, hydroxyl aluminum polymer (Al13), onto the surface of diatomite and heating at various temperatures. The results indicate that Al was incorporated and implanted into the structure of diatomite by the condensation reaction of the hydroxyl groups of Al13 and diatomite, and the Si–O–Al(OH) groups were formed during the condensation reaction. Al incorporation by the condensation reaction of hydroxyl groups of Al13 with single silanols of diatomite occurred more readily than that with geminal silanols. The Al incorporation increased solid acidity of diatomite after Al incorporation. The acidity improvement was various for different types of acid sites, depending on the preparation temperature of the Al-incorporated diatomite. Both Brønsted and Lewis acid sites increased greatly after heating at 250 and 350 °C, but only L acid sites significantly improved after heating at 500 °C. These results demonstrate that the structural incorporation of Al3+ ions into diatomite can occur by the condensation reaction of the hydroxyl groups of the Al precursors and diatomite. Moreover, the rich solid acid sites of Al-incorporated diatomite show its promising application as a solid acid catalyst.

Hierarchically porous TS-1/modified-diatomite composites with high removal efficiency for methylene blue (MB) were prepared via a facile in situ hydrothermal route. The surface charge state of the diatomite was modified to enhance the electrostatic interactions, followed by in situ hydrothermal coating with TS-1 nanoparticles. The zeolite loading amount in the composites could be adjusted by changing the hydrothermal time. The highest specific surface area and micropore volume of the obtained composites were 521.3 m2/g and 0.254 cm3/g, respectively, with an optimized zeolite loading amount of 96.8%. Based on the synergistic effect of efficient adsorption and photocatalysis resulting from the newly formed hierarchically porous structure and improved dispersion of TS-1 nanoparticles onto diatomite, the composites’ removal efficiency for MB reached 99.1% after 2 h of photocatalytic reaction, even higher than that observed using pure TS-1 nanoparticles. Moreover, the superior MB removal kinetics of the composites were well represented by a pseudo-first-order model, with a rate constant (5.28 × 10−2 min−1) more than twice as high as that of pure TS-1 nanoparticles (2.43 × 10−2 min−1). The significant dye removal performance of this novel TS-1/modified-diatomite composite indicates that it is a promising candidate for use in waste water treatment.

Naturally occurring porous diatomite (Dt) was functionalized with phenyltriethoxysilane (PTES), and the PTES-modified diatomite (PTES-Dt) was characterized using diffuse reflectance Fourier transform infrared spectroscopy, nitrogen adsorption, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. After silylation, a functional group (C6H5, phenyl) was successfully introduced onto the surface of Dt. PTES-Dt exhibited hydrophobic properties with a water contact angle (WCA) as high as 120° ± 1°, whereas Dt was superhydrophilic with a WCA of 0°. The benzene adsorption data on both Dt and PTES-Dt fit well with the Langmuir isotherm equation. The Langmuir adsorption capacity of benzene on PTES-Dt is 28.1 mg/g, more than 4-fold greater than that on Dt. Moreover, the adsorption kinetics results show that equilibrium was achieved faster for PTES-Dt than for Dt, over the relative pressure range of 0.118–0.157. The excellent benzene adsorption performance of PTES-Dt is attributed to strong π-system interactions between the phenyl groups and the benzene molecules as well as to the macroporosity of the PTES-Dt. These results show that the silylated diatomite could be a new and inexpensive adsorbent suitable for use in benzene emission control.

•Hierarchically porous nanocomposites with 3D reticulated structure were prepared.•Macroporous structure of diatomite-based support remains intact in the nanocomposite.•Silicalite-1 was in situ and homogeneously coated on surface of ceramic monoliths.•The nanocomposites exhibit high benzene adsorption capacity and mass transfer rate.Novel hierarchically porous nanocomposites of diatomite-based ceramic supports coated with silicalite-1 (Sil-1) nanoparticles for benzene adsorption were prepared via a facile preparation route. In this route, porous ceramic supports with three-dimensional reticulated structures were first prepared using the polymeric sponge method in which diatomite was used as the ceramic framework and polyurethane foam was used as the sacrificial template. This process was followed by facile in situ homogeneous coating of Sil-1 on the surface of the ceramic under mild conditions. The hierarchical porosity of the nanocomposites was due to the inherent micropores of Sil-1, the mesopores resulting from the stacking of Sil-1, and the hierarchical macropores of ceramic supports. The specific area and micropore volume of the nanocomposites were 122.9 m2/g and 0.07 cm3/g, respectively, with a high zeolite loading of 32.4%. The nanocomposites exhibited a much higher benzene adsorption capacity (133.3 mg/g(Sil-1)) compared with that of a commercial micron-sized ZSM-5 product (66.5 mg/g) and a synthesized Sil-1 (SilSYN, 94.7 mg/g). Moreover, adsorption–desorption rate constants of the nanocomposites were three and five times higher than those of the ZSM-5 and SilSYN, respectively, as evaluated via a gravimetric method using an intelligent gravimetric analyzer. The excellent benzene adsorption performance is ascribed not only to the in situ silicalite-1 coating process that facilitates the stability and dispersity of Sil-1 on the modified surface of the ceramic supports but also to the hierarchically porous monolithic structure of the nanocomposites, which is beneficial to the mass transfer efficiency for benzene adsorption.

•Porosity of diatomite-templated carbons was greatly enhanced by KOH activation.•KOH-activated carbons had much larger adsorption capacity than original carbons.•A mesopore-predominant zeolite, zeolite K-H, was prepared as a byproduct.In this study, KOH activation was performed to enhance the porosity of the diatomite-templated carbon and to increase its adsorption capacity of methylene blue (MB). In addition to serving as the activation agent, KOH was also used as the etchant to remove the diatomite templates. Zeolite K-H was synthesized as a byproduct via utilization of the resultant silicon- and potassium-containing solutions created from the KOH etching of the diatomite templates. The obtained diatomite-based carbons were composed of macroporous carbon pillars and tubes, which were derived from the replication of the diatomite templates and were well preserved after KOH activation. The abundant micropores in the walls of the carbon pillars and tubes were derived from the break and reconfiguration of carbon films during both the removal of the diatomite templates and KOH activation. Compared with the original diatomite-templated carbons and CO2-activated carbons, the KOH-activated carbons had much higher specific surface areas (988 m2/g) and pore volumes (0.675 cm3/g). Moreover, the KOH-activated carbons possessed larger MB adsorption capacity (the maximum Langmuir adsorption capacity: 645.2 mg/g) than those of the original carbons and CO2-activated carbons. These results showed that KOH activation was a high effective activation method. The zeolite K-H byproduct was obtained by utilizing the silicon- and potassium-containing solution as the silicon and potassium sources. The zeolite exhibited a stick-like morphology and possessed nanosized particles with a mesopore-predominant porous structure which was observed by TEM for the first time.Graphical abstract

Highlights•Naturally occurring tubular halloysite was used as a mesoporous carrier for the loading of ibuprofen for the first time.•Ibuprofen was primarily encapsulated in the lumen and partially loaded on the external surface of the halloysite.•Organosilane modification of halloysite substantially promoted the loading of ibuprofen.•Heating helped to preserve the lumen space of APTES-modified halloysite and further increased the ibuprofen loading.Natural halloysite with a mesoporous lumen was used as a carrier for the loading of ibuprofen (IBU) for the first time. The halloysite products were characterized by elemental analysis, nitrogen adsorption, X-ray diffraction, diffuse reflectance infrared Fourier transform spectrometry, thermogravimetric analysis, differential scanning calorimetry, solid-state nuclear magnetic resonance, scanning electron microscopy, and transmission electron microscopy. IBU was loaded mainly into the lumen and partially on the external surface of the halloysite. The loaded IBU was present as nanocrystal and amorphous state. In unmodified halloysite, initially the IBU were anchored to the surface hydroxyl groups by hydrogen bonding, and then the added IBU molecules formed aggregates via hydrogen-bonds to the anchored IBU. The surface functionalization of halloysite by 3-aminopropyltriethoxysilane (APTES) promoted the loading of IBU in halloysite. APTES induced a strong affinity through electrostatic attraction, between the carboxyl groups of IBU and the aminopropyl groups of the grafted APTES. In grafted halloysite, a thermal pretreatment at 400 °C reduced the water content leading to a restriction of the APTES oligomerization in the lumen. Consequently, the free lumen space was preserved and resulted in a further increase in IBU loading. The modified halloysite, pretreated by heating and grafted by APTES, had the largest IBU loading, which was 25.4% greater than that in unmodified halloysite.Graphical abstract

In this study, the effects of four types of clay minerals on the thermal decomposition of 12-aminolauric acid (ALA) were investigated. The decomposition temperature of ALA in ALA–clay complexes was in the range of 200–500 °C. The derivative thermogravimetry results indicated that all clay minerals exhibited catalytic activity on the decomposition of ALA. Pure ALA decomposed at approximately 464 °C, a temperature higher than the decomposition temperature of ALA in the presence of clay minerals. The decomposition temperature of ALA in different ALA–clay complexes follows the order illite (452 °C) > kaolinite (419 °C) > rectorite (417 °C) > montmorillonite (400 °C). This order is negatively correlated with the amounts of solid acid sites in the clay minerals, indicating that ALA is catalyzed by the solid acid sites in these minerals.

Hierarchically porous carbons were prepared using a facile preparation method in which diatomite was utilized as both template and catalyst. The porous structures of the carbon products and their formation mechanisms were investigated. The macroporosity and microporosity of the diatomite-templated carbons were derived from replication of diatom shell and structure-reconfiguration of the carbon film, respectively. The macroporosity of carbons was strongly dependent on the original morphology of the diatomite template. The macroporous structure composed of carbon plates connected by the pillar- and tube-like macropores resulted from the replication of the central and edge pores of the diatom shells with disk-shaped morphology, respectively. And another macroporous carbon tubes were also replicated from canoe-shaped diatom shells. The acidity of diatomite dramatically affected the porosity of the carbons, more acid sites of diatomite template resulted in higher surface area and pore volume of the carbon products. The diatomite-templated carbons exhibited higher adsorption capacity for methylene blue than the commercial activated carbon (CAC), although the specific surface area was much smaller than that of CAC, due to the hierarchical porosity of diatomite-templated carbons. And the carbons were readily reclaimed and regenerated.Graphical abstractHighlights► Templated carbon obtained by using surface solid acidity and morphology of diatomite. ► The carbon with macroporous structure composed of carbon tubes and pillars. ► The carbon with good adsorption capacity of methylene blue and regenerability.

Zerovalent iron nanoparticles have been successfully synthesized using sodium borohydride solution reduction of ferric trichloride hexahydrate in the presence of montmorillonite as an effective protective reagent and support as well. A combination of characterizations reveals that with high monodispersity these obtained iron nanoparticles are well dispersed on clay surface, virginal from boron related impurity, and oxidation resistant well with iron core-iron oxide shell structure. The shell thickness of 3 nm remains almost invariable under ambient conditions. The size control of these iron nanoparticles has been achieved by tailoring the amount of the ferric iron, which mainly depends on the protective action of montmorillonite.

The inherent or enhanced solid acidity of raw or activated diatomite is found to have significant effects on the synthesis of hierarchically porous diatomite-templated carbon with high surface area and special porous structure. The solid acidity makes raw/activated diatomite a catalyst for the generation of porous carbon, and the porous parameters of the carbon products are strongly dependent on the solid acidity of diatomite templates. The morphology of diatomite also dramatically affects the textural structure of porous carbon. Two types of macroporous structures in the carbon product, the partially solid pillars and the ordered hollow tubes, derive from the replication of the central and the edge pores of diatom shell, respectively. The hierarchically porous carbon shows good capability for the adsorption of solvent naphtha and H2, enabling potential applications in adsorption and gas storage.

Fe-PILC samples were synthesized by the reaction between Na+- and/or Ca2+-montmorillonite (Mt) and base-hydrolyzed solutions of Fe(III) nitrate. Different from the known usual microporous pillared structure, a meso–microporous delaminated structure containing intercalated or pillared fragments was found in the respective resulting Fe-intercalated or -pillared clays. XRD patterns of Na+-Mt-based Fe-intercalated/pillared clays show one large d-spacing above 6.4 nm corresponding to the mesoporous delaminated part, whereas another d-spacing of ca. 1.5 nm was indicative of the microporous pillared part. Fe-intercalated/pillared clays based on Ca2+-Mt lead to similar results, but with a d-spacing less than 6 nm and a second low intense d-spacing less than 1.5 nm. In the delaminated Fe-intercalated clays, NO−3 anions were retained even after thorough washing process. They play as counterions to neutralize the positive-charged iron aggregates in the delaminated structure, and can be exchanged by heteropolyanions as [PW12O40]3−. The delaminated Fe-pillared clays show good thermal stability at 500 °C and exhibit at this temperature dramatically higher specific surface area and porosity than the starting montmorillonites. However, calcination at a higher temperature leads to the formation of nanocrystalline hematite. Air-drying after ethanol extraction (EAD) method has an advantage over air-drying (AD) method in preserving the delaminated structure.Schematic representation of the structure of delaminated Fe-intercalated/pillared montmorillonite, which consists of a mesoporous delaminated structure containing microporous intercalated or pillared fragments.

In the present work, iron pillared clays were synthesized by the reaction of montmorillonite with base-hydrolyzed solutions of Fe(III) nitrate. In contrast with the classical microporous pillared structure, a novel meso–microporous delaminated structure containing pillared fragments in iron-pillared clay was obtained. A considerable amount of NO3- is found to be retained in the resultant delaminated iron-pillared clays even after thorough washing by successive agitations/centrifugations. This amount is closely related with the content of the iron species in the iron-pillared clays. The highest BET specific surface area and the largest porosity of the delaminated iron pillared clays are 215.7 m2/g and 0.29 ml/g, respectively. Mesopores in the delaminated structure make the main contribution to the total surface area and porosity, and most of them are preserved after calcination at 773 K. These fundamental results are of importance in developing novel heterogeneous catalysts and adsorbents.

Diatomaceous amorphous silica samples were modified by silylation using trimethylchlorosilane (TMCS). The resultant materials were characterized by using thermogravimetry (TG), 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR), Fourier transform infrared spectroscopy (FTIR) and chemical analysis. The degree of silylation was found to increase with the increasing temperature of thermal pretreatment on diatomaceous silica prior to silylation. Increment of the pretreated temperature leads to stepwise removal of physisorbed water followed by the dehydration of capping water that H-bonded with the surface silanols, resulting in exposure of more and more isolated and H-bonded silanols previously covered by water molecules. Among these exposed silanols, isolated silanols show high activity for silylation reaction but H-bonded ones show poor activity. The maximum degree of surface attachment of TMCS grafted onto the diatomaceous silica (about 1.81 mmol TMCS groups per gram of silica) was shown in the sample pretreated at 1100 °C, in which the amount of exposed isolated silanols get the maximum. The fundamental information derived from this work is of significance in well understanding the surface silylation reaction of diatomaceous silica and providing useful information for related industrial production.

The network characteristic of a selection of diatomaceous silica derived from China has been investigated using Raman spectroscopy. Before any thermal treatment of the sample, two prominent bands of 607 and circa 493 cm−1 are resolved in the Raman spectra of diatomaceous silica, corresponding to the (SiO)3-ring breathing mode of D2-line and the O3SiOH tetrahedral vibration mode of D1-line, respectively. This is more similar to the pyrogenic silica rather than the silica gel. For the latter, to obtain a (SiO)3-ring, the sample must be heated between 250 and 450 °C. Significant difference is also found between the diatomaceous silica and other natural silicas, e.g. in the Raman spectra of sedimentary and volcanic opals, neither D1 nor D2 band is detected in previous reports.

•Novel hierarchical diatomite zeolite composites prepared by a NaOH etching method.•NaOH etching enlarged macropores of frustule and increased coated zeolite contents.•The composites exhibited good macro-/microporosity and high specific surface area.•The composites exhibited excellent performance for benzene adsorption.Hierarchically porous diatomite/MFI-type zeolite (Dt/Z) composites with excellent benzene adsorption performance were prepared. The hierarchical porosity was generated from the microporous zeolite coated at the surface of diatom frustules and from the macroporous diatomite support. A facile NaOH etching method was employed for the first time to treat the frustule support, followed by hydrothermal growth of MFI-type zeolite at the surface of frustules previously seeded with nanocrystalline silicalite-1 (Sil-1). NaOH etching enlarged the pores on diatom frustules and further increased the coated zeolite contents (Wz). The central macropore size of the diatom frustules increased from approximately 200–500 nm to 400–1000 nm after NaOH etching. The Wz could reach 61.2%, while the macroporosity of the composites was largely preserved due to more voids for zeolite coating being formed by NaOH etching. The Dt/Z composites exhibited higher benzene adsorption capacity per unit mass of zeolite and less mass transfer resistance than Sil-1, evaluated via a method of breakthrough curves. These results demonstrate that etching of a diatomite support is a facile but crucial process for the preparation of Dt/Z composites, enabling the resulting composites to become promising candidates for uses in volatile organic compounds emission control.