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A very green catalytic method has been introduced for the synthesis of alkylaromatic ketones by solvent-free benzylic oxidation of alkylaromatics with molecular oxygen (O2) over hexagonally mesostructured MnSBA-15 catalysts synthesized with a variety of manganese (Mn) contents using a pH-adjusting direct hydrothermal (pH-aDH) method. For example, the solvent-free oxidation of ethylbenzene (EB) over different mesoporous MnSBA-15 catalysts and uniform pore sized MnMCM-41(31) prepared by an alkaline hydrothermal method has been systematically evaluated. Washed MnSBA-15(4) (W-MnSBA-15(4)) or green mesoporous MnSBA-15(4) obtained after the removal of the non-framework octahedral Mn2O3 species deposited on the active surface of MnSBA-15(4) using a promising chemical treatment method is used for this reaction to evaluate its catalytic activity. Meanwhile the recyclability and hot-filtration experiments for this reaction have been also studied. The catalytic activities obtained from the above catalytic results prove that the W-MnSBA-15(4) has higher EB conversion and AP[double bond, length as m-dash]O selectivity than the other mesoporous catalysts used in this reaction. Therefore, in order to find the optimal reaction parameters for this reaction, various reaction parameters with W-MnSBA-15(4) have been thoroughly evaluated. Using W-MnSBA-15(4), the catalytic results obtained with different oxidants used in this reaction have also been discussed clearly. The catalytic results of solvent-free benzylic oxidations with W-MnSBA-15(4) conducted with different alkylaromatic molecules have been obviously discussed. All the mesoporous catalysts used in this reaction have been characterized using several instrumental techniques to confirm them as the standard mesoporous catalysts. The plausible reaction mechanism for the solvent-free oxidation of EB has been successfully reported based on the characterization results of the catalyst and catalytic results. The ESR and UV-vis DRS results of the W-MnSBA-15 catalyst used in these reactions corroborate that the disordered octahedral divalent (Mn2+) and tetrahedral trivalent (Mn3+)-species have been successfully incorporated on the silica surface of the catalysts. Based on the catalytic results, it is noteworthy to observe that mesoporous W-MnSBA-15(4) is a highly active, green and promising heterogeneous catalyst for the selective synthesis of alkylaromatic ketones, since the catalyst produces the best catalytic activity among the other mesoporous Mn silicate catalysts.

A non-thermal dielectric barrier discharge (DBD) plasma reactor was integrated with an M/SBA-15 (M = Pd, Pt, Ag and Au) catalyst, where metal reduction was achieved by H2 plasma treatment. Subsequently, the plasma-catalytic combination mode was tested for the methane partial oxidation reaction to liquid oxygenates, and the results were compared with the plasma-only system in terms of reactant conversion, energy efficiency and product distribution. The results from the characterization of the catalysts confirmed that the plasma treatment improved the surface characteristics of the catalysts and also modified or expanded the discharge on the catalytic surface. The plasma energetic species generally helped to flatten the metal nanoparticles over the support surface, which resulted in a better dispersion with the formation of smaller nanoparticles. A total liquid selectivity of 70% was achieved for the plasma-treated Pt/SBA-15-DBD system with almost 12% CH4 conversion compared to 58% total liquid at 7% CH4 conversion with the plasma-only system.

Mercury contamination is one of the major environmental and health issues that has been affecting our lives for several decades. To address this matter, a rational design of robust adsorbent materials bearing chelating sites for binding with Hg2+ is highly desirable. Porous organic materials have recently emerged as excellent adsorbent materials for heavy metal ions and toxic gases. These porous nanomaterials are generally synthesized via bottom-up chemical reactions, which offer ample opportunities for modifying their structure through the incorporation of various functional sites, thereby, rendering them as an essential platform for designing flexible materials with numerous applications. Scalable synthetic approaches, together with high specific surface area and robustness of framework distinguishes porous organic materials, such as porous organic polymers (POPs) and covalent organic frameworks (COFs), as versatile and indispensable nanoscale materials along with other frontline porous materials including porous carbons, zeolites, aluminophosphates, metal–organic frameworks (MOFs), functionalized mesoporous silica, and periodic mesoporous organosilicas (PMOs). It is worthy to mention that a tailorable structural design approach of POPs and COFs offer adjustable surface property in terms of specific surface area, pore size, and functionality, which can be advantageous towards achieving a benchmark adsorbent material for the detoxification of wastewater to counter harmful environmental effects. Although POPs/COFs are outstanding in removing mercury from contaminated water, to the best of our knowledge, till date, there is hardly any comprehensive review that exclusively highlights all such discoveries. In this review, we highlight some major achievements in the synthesis of porous organic materials and their potential as adsorbents for the removal of Hg(II) from different water resources including actual conditions together with their future potential in water purification technologies.

Correction for ‘green synthesis of silver nanoparticles using plant extracts and their antimicrobial activities: a review of recent literature’ by Chhangte Vanlalveni et al., RSC Adv., 2021, 11, 2804–2837, https://doi.org/10.1039/D0RA09941D.

Correction for ‘A review of the recent progress on heterogeneous catalysts for Knoevenagel condensation’ by Jimmy Nelson Appaturi et al., Dalton Trans., 2021, 50, 4445–4469, DOI: 10.1039/d1dt00456e.

Aluminium-containing spherical mesoporous silica nanoparticle (AlSMSN) materials were synthesized for the first time using cetyltrimethylammonium bromide (CTMABr) as a structure-directing agent under nonhydrothermal conditions at room temperature. The effect of the nature of the Al source on the synthesis of the AlSMSN materials was investigated using a variety of Al sources. The effect of higher Al ion incorporation on the structural and textural properties of the AlSMSN materials was evaluated by varying the nSi/nAl ratios, and an efficient chemical treatment method was developed for the removal of superficial octahedral Al ions from the surface of the AlSMSN materials. The synthesized AlSMSN materials were characterized using ICP-AES, XRD, N2 adsorption, 27Al & 29Si MAS NMR, FTIR, TEM, and FE-SEM techniques. ICP-AES results revealed incorporation of a high Al ion content (nSi/nAl = 24) into the spherical mesoporous silica nanoparticle materials. For all of the calcined AlSMSN materials, the XRD reflection peaks shifted to lower angle with increasing Al ion content, resulting in an increase of the unit cell parameter. The textural parameters of the AlSMSN materials, except for the surface area, found from nitrogen adsorption measurements, increase with an increase in the amount of aluminium isopropoxide in the synthesis gel. The location and coordination of Al ions on the walls of the AlSMSN materials and the amount of Al ions incorporation were determined from the 27Al MAS NMR measurements. TEM and FE-SEM images demonstrated that the AlSMSN materials comprise spherical particles with hexagonally packed uniform mesoporous channels. Furthermore, the AlSMSN(20) with a higher Al content exhibits better hydrothermal stability than the AlSMSN(100) congener with a lower Al content. Catalyst recyclability studies showed that the washed catalyst (W-AlSMSN(20)) exhibited exceptional catalytic activity during t-butylation of phenol with 95.4% 4-t-butylphenol (4-TBP) selectivity due to removal of superficial octahedrally coordinated Al ions on the surface of active sites.

The incessant formation of chain-like IBN-4 mesoporous silica (ICMS-N) with long channels running along the length of hexagonal rods have been directly achieved by the co-condensation of 3-aminopropyltriethoxysilane (APTES) and tetraethylorthosilicate as the silica source in the presence of Pluronic P123 and fluorocarbon (FC-4) surfactants as structure directing agents. The newly synthesized materials were successfully characterized using SAXS, N2-physisorption, FT-IR, XPS, 29Si NMR, TEM, SEM and elemental analysis. TEM images confirmed the chain-like morphologies, whereas SEM studies showed that the synthesized ICMS-N particles possess length >10 μm. Moreover, the as-formed material was tested for the removal of oxyanions such as arsenate and chromate, and it exhibited the maximum adsorption capacity of 55 and 35 mg g−1 for ICMS-N15, respectively. The formation of quaternary species of amine on the surface of the ICMS-N enhanced the adsorption capacity towards arsenate and chromate under acidic pH and the adsorption isotherm fits with Langmuir monolayer adsorption. Naturally, existing anions such as nitrate, sulfate, phosphate and chlorides with 1 × 10−2 M have no significant effect on the adsorption of heavy metal ions; moreover, reusability tests were also carried out.

Novel hierarchically dispersed spherical mesoporous silica (HSMS) was synthesized using a surfactant mixture of fluorocarbon (FC-4), cetyl-trimethyl ammonium bromide (CTAB), and block copolymer Pluronic F127 (PF127). To prepare the thiol-functionalized HSMS (T-HSMS), the synthesized HSMS was functionalized by a co-condensation method using 3-mercaptotrimethoxysilane (3-MPS) as a thiol reagent. The obtained HSMS and T-HSMS possess a cubic morphology with a lmm space group and a particle diameter of 75–200 nm. The HSMS and T-HSMS materials exhibit large free surface areas exceeding 844 and 663 m2 g−1 and pore radii of approximately 3.2 and 3.1 nm, respectively. The synthesized materials were characterized using small angle X-ray scattering, N2-physisorption studies, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy studies. The efficacy of mercury adsorption by T-HSMS was studied at different temperatures, 283, 298, and 313 K. The obtained results were fitted with a Langmuir adsorption isothermal plot. The changes in the negative Gibbs free energy values for the spontaneity of the process were calculated. Mercury could be successfully desorbed using thiourea in a 2 M HCl solution, and the adsorbents could be subsequently reused without severe loss of their activity after repeated adsorption tests.

A series of vanadia-doped iron-oxide-pillared clays (V/Fe-PILCs) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H(2)S was investigated. V/Fe-PILCs were characterized using X-ray diffraction (XRD), surface area- and pore volume measurements, chemical analysis, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H(2) (H(2)-TPR). V/Fe-PILCs showed better catalytic performance than Fe-PILC without any significant SO(2) emissions. The H(2)S conversion over V/Fe-PILCs increased with increasing vanadia content up to 7 wt.%. However, it decreased at higher vanadia loading due to the decrease in surface area and the formation of the crystalline V(2)O(5) phase. The presence of water vapor in the reactant mixture resulted in a decrease of H(2)S conversion.

Two-dimensional hexagonal thick-walled mesoporous titanosilicate catalysts synthesized using various amounts of titanium were used for the synthesis of 2,3,5-trimethyl-1,4-benzoquinone (TMBO) by liquid-phase oxidation of 2,3,6-trimethylphenol (TMP–OH). These catalysts were also used for the oxidation of di-/tri-substituted phenols to produce 2,6-disubstituted p-benzoquinones (DSBQs). A promising chemical treatment method, for the preparation of green mesoporous TiSBA-15(6) or Washed TiSBA-15(6), was used for removal of non-framework TiO2 nanoparticle species from the active surface, and the catalytic activity of the recovered mesoporous TiSBA-15(6) catalyst has been evaluated. To confirm the green aspects, recyclability and hot-catalytic filtration experiments were performed. Based on the experimental results, it was found that the green mesoporous TiSBA-15(6) is a highly active, recyclable, and promising heterogeneous catalyst for the selective synthesis of TMBO and DSBQs and produces >99% TMBO selectivity with 100% TMP–OH conversion at 353 K for 60 min and 90–100% DSBQs selectivity with 83–99% phenol conversion at 330 K for 1–5 h.

This paper reports the effectiveness of carrying out the cycloaddition reaction of styrene oxide (SO) and CO2 without the use of any catalysts. A naturally abundant and cheap material, urea, was utilized in promoting the reaction by controlling the reaction conditions. The influence of reaction temperature, carbon dioxide (CO2) pressure, amount of urea, and the reaction time on the selectivity of styrene carbonate (SC) was investigated.

Well hexagonally ordered NbSBA-15 catalysts synthesized by an efficient hydrothermal method were used, for the first time, for the selective synthesis of vitamin K(3) by liquid-phase oxidation of 2-methyl-1-naphthol (2MN1-OH) under various reaction conditions. The recyclable NbSBA-15 catalysts were also reused to find their catalytic activities. To investigate the leaching of non-framework niobium species on the surface of silica networks, the results of original and recyclable NbSBA-15 catalysts were correlated and compared. To find an optimum condition for the selective synthesis of vitamin K(3), the washed NbSBA-15(2.2pH) was extensively used in this reaction with various reaction parameters such as temperature, time and ratios of reactant (2M1N-OH to H(2)O(2)), and the obtained results were also demonstrated. Additionally, the liquid-phase oxidation of 2M1N-OH was carried out with different solvents to find the best solvent with a good catalytic activity. Based on the all catalytic studies, the vitamin K(3) selectivity (97.3%) is higher in NbSBA-15(2.2pH) than that of other NbSBA-15 catalysts, and the NbSBA-15(2.2pH) is found to be a highly active and eco-friendly heterogeneous catalyst for the selective synthesis of vitamin K(3).

The step-up synthesis of amidoxime-functionalised periodic mesoporous organosilicas (PMOs) with an ordered hexagonal structure was achieved in two steps: (i) direct co-condensation of diaminomaleonitrile and 3-isocyanatopropyltriethoxysilane (IPTES) and (ii) chemical modification of bridged nitrile into amidoxime using a hydroxylamine hydrochloride (NH2OH·HCl) reagent. The synthesis approach allowed a high loading of amidoxime functional groups in the pore wall framework of the mesoporous materials with controlled regular morphologies. The resulting materials with various diureylenemaleonitrile contents (up to 40 mol%) contained ordered hexagonal mesopores. The highly ordered hexagonal arrangement of the pores with a high degree of uniformity of amidoxime-functionalised PMOs was confirmed by low-angle X-ray diffraction (XRD), N2 adsorption isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition of the mesoporous organosilica was further characterised by Fourier transform infrared (FT-IR) spectroscopy, 29Si magic angle spinning (MAS) and 13C cross-polarization (CP) MAS nuclear magnetic resonance (NMR) spectroscopy. The synthesised materials with an amphoteric ligand in the framework were found to be suitable carrier materials for controlled drug delivery systems in a phosphate buffer solution at pH 6.0, 7.4 and 9.0 for both hydrophobic (ibuprofen) and hydrophilic drugs (5-fluorouracil).

Two-dimensional SnSBA-15(CVD) catalyst was synthesized by the chemical vapor deposition (CVD) method using calcined SBA-15 with anhydrous tin(IV) chloride. For comparison studies, two mesoporous tin silicate catalysts, Sn/SBA-15(SC) and Sn/SBA-15(SA) were synthesized under the incipient wetness impregnation (IWI) method using calcined SBA-15 with different tin sources. SnMCM-41(40) was also synthesized by basic hydrothermal conditions. The synthesized mesoporous catalysts were characterized by ICP-AES, XRD, N2 adsorption, UV vis DRS, 29Si MAS NMR, FE-SEM and TEM for the proof of standard mesoporous catalysts with nature of tin on the silica pore walls. For highly selective synthesis of nopol (N–OH), the Prins condensation of β-pinene (PE) with paraformaldehyde (PF-CHO) was performed over different mesoporous catalysts such as SiSBA-15, SnSBA-15(CVD), Sn/SBA-15(SC), SnSBA-15(SA) and SnMCM-41(40), and it was conducted using a variety of optimal parameters such as amount of catalyst, reaction time, reaction temperature, ratios of reactant (PE/PF-CHO), solvents and recycles. In addition, SnSBA-15(CVD) was used in the Prins condensation of PE with PF-CHO in the presence of propyl cyanide (PrCN) with water to investigate its catalytic activity. On the basis of all catalytic results, SnSBA-15(CVD) is found to be a highly active, water-resistant and recyclable heterogeneous catalyst for selective synthesis of N–OH.