Fine bubble technology for the green synthesis of fairy chemicals.

Fairy chemicals (FCs), such as 2-azahypoxanthine (AHX), are a potential new class of plant hormones that are naturally present in plants and produced via a novel purine metabolic pathway. FCs support plant resilience against various stresses and regulate plant growth. In this study, we developed a four-step method for synthesising AHX from 2-cyanoacetamide, achieving a good yield. Oxime was obtained from 2-cyanoacetamide via the oximation reaction. Cascade-type one-pot selective Pt/C-catalysed reduction of oxime, followed by a coupling reaction with formamidine acetate, yielded intermediate 5-amino-1H-imidazole-4-carboxamide (AICA). For the synthesis of AICA from oxime, we used modern fine bubble technology, affording AICA in 69% yield. Subsequently, we synthesised 4-diazo-4H-imidazole-5-carboxamide (DICA) from AICA via the diazotisation reaction. Notably, the synthesis of DICA from AICA was achieved, and the stability of previously known less stable DICA in the solid state was confirmed. Finally, PhI(OAc)2 (0.5 mol%) catalysed the intramolecular cyclisation of DICA in the green solvent water to yield AHX (overall yield of 47%). This study's innovative techniques and substantial discoveries highlight its potential influence and significance in FC science, thereby establishing a new standard for subsequent research.

Rod-Shaped Spinel Co3O4 and Carbon Nitride Heterostructure-Modified Fluorine-Doped Tin Oxide Electrode as an Electrochemical Transducer for Efficient Sensing of Hydrazine.

Engineering low-cost and efficient materials for sensing hydrazine (HA) is critical given the adverse effects of high concentrations on humans. We report an efficient electrode made up of rod-shaped Co3O4/g-C3N4 (Co3O4/graphitic carbon nitride (GCN))-coated fluorine-doped tin oxide as a desirable electrode for the detection of HA. GCN is synthesized by the thermal decomposition of melamine, Co3O4, and the heterostructure is grown by a hydrothermal process. The as-prepared materials were characterized by using spectroscopic and microscopic techniques. The voltammetric studies showed that HA can be oxidized at a lower onset potential of 0.24 V vs reference Ag/AgCl, and the composite yielded a significantly enhanced oxidation peak current than the pure components because of the high electrocatalytic activity and the synergy between Co3O4 and GCN. By employing chronoamperometry, the proposed sensor can detect HA in a wide range with a high sensitivity of 819.52 µA mM-1 cm-2 and a detection limit of 3.14 µM. The high conductivity of Co3O4, enhanced electroactive surface area, the rich redox couples of Co2+/Co3+, and the additional catalytic sites from GCN are responsible for the high performance of the heterostructure.

Highly Luminescent and Stable Halide Perovskite Nanocrystals by Interfacial Defect Passivation and Amphiphilic Ligand Capping.

Halide vacancies cause lattice degradation and nonradiative losses in halide perovskites. In this study, we strategically fill bromide vacancies in CsPbBr3 perovskite nanocrystals with NaBr, KBr, or CsBr at the organic-aqueous interface for hydrophobic ligand-capped nanocrystals or in a polar solvent (2-propanol) for amphiphilic ligand-capped nanocrystals. Energy-dispersive X-ray spectra, powder X-ray diffraction data, and scanning transmission electron microscopy images help us confirm vacancy filling and the structures of samples. The bromide salts increase the photoluminescence quantum yield (98 ± 2%) of CsPbBr3 by decreasing the nonradiative decay rate. Single-particle studies show the quantum yield increase originates from the poorly luminescent nanocrystals becoming highly luminescent after filling vacancies. Furthermore, we tune the optical band gap (ultraviolet-visible-near-infrared) of the hydrophobic ligand-capped nanocrystals by halide exchange at the toluene-water interface using saturated NaCl or NaI solutions, which completes in about 60 min under continuous mixing. In contrast, the amphiphilic ligand accelerates the halide exchange in 2-propanol, suggesting ambipolar functional groups speed up the ion-exchange reaction. The bromide vacancy-filled or halide-exchanged samples in a toluene-water biphasic solvent show higher stability than amphiphilic ligand-capped samples in 2-propanol. This strategy of defect passivation, ion exchange, and ligand chemistry to improve quantum yields and tune band gaps of halide perovskite nanocrystals can be promising for designing stable and water-soluble perovskite samples for solar cells, light-emitting diodes, photodetectors, and photocatalysts.

Hybridization of Co3S4 and Graphitic Carbon Nitride Nanosheets for High-performance Nonenzymatic Sensing of H2O2.

The development of efficient H2O2 sensors is crucial because of their multiple functions inside and outside the biological system and the adverse effects that a higher concentration can cause. This work reports a highly sensitive and selective non-enzymatic electrochemical H2O2 sensor achieved through the hybridization of Co3S4 and graphitic carbon nitride nanosheets (GCNNS). The Co3S4 is synthesized via a hydrothermal method, and the bulk g-C3N4 (b-GCN) is prepared by the thermal polycondensation of melamine. The as-prepared b-GCN is exfoliated into nanosheets using solvent exfoliation, and the composite with Co3S4 is formed during nanosheet formation. Compared to the performances of pure components, the hybrid structure demonstrates excellent electroreduction towards H2O2. We investigate the H2O2-sensing performance of the composite by cyclic voltammetry, differential pulse voltammetry, and amperometry. As an amperometric sensor, the Co3S4/GCNNS exhibits high sensitivity over a broad linear range from 10 nM to 1.5 mM H2O2 with a high detection limit of 70 nM and fast response of 3 s. The excellent electrocatalytic properties of the composite strengthen its potential application as a sensor to monitor H2O2 in real samples. The remarkable enhancement of the electrocatalytic activity of the composite for H2O2 reduction is attributed to the synergistic effect between Co3S4 and GCNNS.

Solvent-free benzylic oxidation of aromatics over Cu(II)-containing propylsalicylaldimine anchored on the surface of mesoporous silica catalysts.

A sustainable method was used to produce aromatic ketones by the solvent-free benzylic oxidation of aromatics over mesoporous Cu(II)-containing propylsalicylaldimine anchored on the surface of Santa Barbara Amorphous type material-15 (CPSA-SBA-15) catalysts. For comparison, mesoporous Cu(II)-containing propylsalicylaldimine anchored with Mobil Composition of Matter-41 (CPSA-MCM-41) was assessed for these reactions under similar reaction conditions. The washed CPSA-SBA-15(0.2) (W-CPSA-SBA-15(0.2)) catalyst was prepared using an easy chemical method for the complete removal of non-framework CuO nanoparticle species on the surface of pristine CPSA-SBA-15(0.2) (p-CPSA-SBA-15(0.2) prepared with 0.2 wt% of Cu, and its catalytic activity was evaluated with different reaction parameters, oxidants and solvents. In order to confirm the catalytic stability, the recyclability was assessed, and the performance of hot-filtration experiments was also evaluated. All the catalysts used for these catalytic reactions were characterized using many instrumental techniques to pinpoint the mesoporous nature and active sites of the catalysts. The proposed reaction mechanism has been well documented on the basis of catalytic results obtained for solvent-free oxidation of aromatics. Based on the catalytic results, we found that W-CPSA-SBA-15(0.2) is a very ecofriendly catalyst with exceptional catalytic activity.

ZnAlMCM-41: a very ecofriendly and reusable solid acid catalyst for the highly selective synthesis of 1,3-dioxanes by the Prins cyclization of olefins.

The Prins cyclization of styrene (SE) with paraformaldehyde (PFCHO) was conducted with mesoporous ZnAlMCM-41 catalysts for the synthesis of 4-phenyl-1,3-dioxane (4-PDO) using a liquid phase heterogeneous catalytic method. For a comparison study, the Prins cyclization reaction was also conducted over different nanoporous catalysts, e.g. mesoporous solid acid catalysts, AlMCM-41(21) and ZnMCM-41(21), and microporous catalysts, USY, Hß, HZSM-5, and H-mordenite. The recyclable mesoporous ZnAlMCM-41 catalysts were reused in this reaction to evaluate their catalytic stabilities. Since ZnAlMCM-41(75) has higher catalytic activity than other solid acid catalysts, washed ZnAlMCM-41(75)/W-ZnAlMCM-41(75) was prepared using an efficient chemical treatment method and used with various reaction parameters to find an optimal parameter for the highly selective synthesis of 4-PDO. W-ZnAlMCM-41(75) was also used in the Prins cyclization of olefins with PFCHO and formalin (FN, 37% aqueous solution of formaldehyde (FCHO)) under different reaction conditions to obtain 1,3-dioxanes, which are widely used as solvents or intermediates in organic synthesis. Based on the nature of catalysts used under different reaction conditions, a reasonable plausible reaction mechanism for the Prins cyclization of SE with PFCHO is proposed. Notably, it can be seen from the catalytic results of all catalysts that the W-ZnAlMCM-41(75) catalyst has higher 4-PDO selectivity with exceptional catalytic activity than other microporous and mesoporous catalysts.

Green oxidation of alkylaromatics using molecular oxygen over mesoporous manganese silicate catalysts.

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 facile method to decompose CO2 using a g-C3N4-assisted DBD plasma reactor.

The present study accomplishes the partial reduction of CO2 to carbon monoxide in a dielectric barrier discharge (DBD) reactor packed with g-C3N4 and TiO2 or ZnO mixed with g-C3N4. Typical results indicate that the ZnO + g-C3N4 packed reactor provides ~12% CO2 conversion at SIE of 4.8 J/mL, whereas DBD yields only ~7.5% conversion under the same experimental conditions. The best performance of the ZnO integrated system is due to the presence of more basic sites than those of the TiO2 packed system, which enables effective adsorption of acidic CO2 on its surface. The highest energy efficiency of 1.106 mmol/kJ is achieved with 5% ZnO + g-C3N4 at SIE of 4.8 J/mL, whereas DBD exhibits only 0.746 mmol/kJ under the same conditions. Notably, catalyst packing also enables the highest carbon balance of ~97%.

Novel ultra-small Pd NPs on SOS spheres: a new catalyst for domino intramolecular Heck and intermolecular Sonogashira couplings.

We report a novel catalyst Pd/SOS that catalyzes the dual C-C bond forming coupling of an iodoarene moiety with an internal alkene and an external alkyne via an intramolecular Heck reaction, followed by an intermolecular Sonogashira reaction, respectively. The catalyst was characterized using XRD, IR, XPS, SEM and TEM analyses. Notably, for the first time, cheap and readily available new silica [nanosilica on microsilica (SOS)] material-supported ultra-small Pd nanoparticles (2.20 nm) are employed for the efficient synthesis of dihydrobenzofuran and oxindole derivatives in a domino one-pot reaction. Significantly, a sub-molar quantity of Pd (0.3 mol%) was found to be sufficient to furnish the products in very good to near quantitative yields. Gratifyingly, the catalyst could be recycled up to five cycles with a marginal loss (∼no loss) of the product.

Reduced graphene oxide supported ZnO quantum dots for visible light-induced simultaneous removal of tetracycline and hexavalent chromium.

Semiconducting nanomaterials play an important role in the photocatalytic removal of aqueous pollutants like heavy metals, organic compounds, pathogens and antibiotics. In this study, we prepared ZnO quantum dots (QD) by the precipitation method and ZnO/rGO materials with varying percentages (0.5-2 wt%) of ZnO were prepared by the hydrothermal method. The synthesized catalysts were characterized by various physicochemical techniques, such as powder X-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible-diffuse reflectance spectroscopy (UV-VIS-DRS), Transmission Electron Microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR) and Brunauer-Emmett-Teller (BET) analysis to determine the structural as well as textural and surface properties. The photocatalytic activity of the prepared catalysts was analyzed during the individual and simultaneous removal of tetracycline (TC) and hexavalent chromium [Cr(vi)] in aqueous medium. Among all the catalysts, 1.5 wt% ZnO/rGO showed the highest visible light activity, where 68% tetracycline and 84% Cr(vi) abatement was observed after 120 min irradiation time. Moreover, tetracycline showed 70% mineralization. The photocatalytic activity is explained based on the photo-generated electron transfer from the conduction band (CB) of ZnO to the surface of rGO which prevents the recombination of excitons and produces OH˙ and O2 -˙; these radicals play an important role in degrading the TC and Cr(vi). The mechanism suggested that the co-existence of oxidizable and reducible species such as TC and Cr(vi) ensured the effective use of the photo-generated electrons and holes that leads to the efficient oxidation of TC and Cr(vi) reduction.

Non-thermal atmospheric pressure plasma jet for the bacterial inactivation in an aqueous medium.

This study reports the potential of non-thermal atmospheric pressure plasma jet for the bacterial inactivation in an aqueous medium. All experiments were conducted in a reactor containing aqueous solution i.e., water, pre-inoculated with bacterial suspensions and after plasma exposure solution is inoculated in Petrifilm to know the viable count. The plasma jet exposure to the bacterial aqueous solution was carried out under various gases such as helium, argon, air and also in combination as Argon + Air and Helium + Air. In each case, the oxidizing species such as hydrogen peroxide, nitric acid, hydroxyl radicals and ozone formed in the reactor during the plasma exposure were quantified. The effect of applied voltage and gas flow rate were studied to optimize the conditions for its efficacy. The solution pH plays a prominent role in bacterial inactivation, as the process is effective at low pH exhibiting 7 log reduction of bacterial population. The bacterial inactivation is efficient at below the critical pH (<4.7) and the inactivation process becomes less effective if the pH goes above 4.7. Plasma treatment of deionized water produces some reactive species such as hydrogen peroxide and nitrates, this plasma treated water is used to test the bacterial inactivation. Addition of Fe2+ salt to the plasma treated water improves the efficacy by converting hydrogen peroxide to hydroxyl radicals, which serves to be a major contributor to the bacterial inactivation. Especially, Non-thermal plasma offers an alternative way to sterilize vacuum sensitive and thermo-labile living tissues.

Enhanced photocatalytic and antibacterial activity of plasma-reduced silver nanoparticles.

A non-thermal atmospheric pressure plasma jet has been used for the green synthesis of highly dispersed colloidal silver nanoparticles. The reducing species such as hydrogen radicals and hydrated electrons are identified, and the change in the solution pH is studied during AgNP formation. The structural properties and size of the plasma-reduced silver nanoparticles are characterized via X-ray diffraction, ultraviolet-visible spectroscopy, fluorescence spectroscopy and transmission electron microscopy. The size of the colloidal AgNPs is tuned by adjusting the initial concentration of AgNO3. The effect of terephthalic acid, a hydroxyl radical scavenger, on the reduction of Ag+ ion is studied. The typical catalytic activity data indicate the better performance of the plasma-reduced colloidal Ag nanoparticles than that obtained from the chemical reduction method. The antibacterial activity of the plasma-reduced Ag nanoparticles also shows a better performance than that of the chemically reduced AgNPs, highlighting the potential of the plasma reduction approach for the synthesis of metal nanoparticles, which are stable even after 30 days without a stabilizing agent. Additionally, the effects of hydroxyl scavengers (isopropyl alcohol) and Fenton's reagent (Fe2+ salt) on CV degradation are studied.

Recyclable Pd/CuFe2O4 nanowires: a highly active catalyst for C-C couplings and synthesis of benzofuran derivatives.

Pd/CuFe2O4 nanowire-catalyzed cross coupling transformations are described. Notably, these reactions showed excellent functional group tolerance. Further, the protocol is applied to a one-pot synthesis of benzofurans via a Sonogashira coupling and intramolecular etherification sequence. The catalyst was reused and found to maintain its activity and stability.

Degradation of malachite green by dielectric barrier discharge plasma.

Oxidative decomposition of aqueous organic pollutant malachite green (MG) was studied in a dielectric barrier discharge reactor operated under ambient conditions. Total organic carbon content analysis confirmed the mineralization of the pollutant leading to the formation of carbon dioxide, which was confirmed by an infrared analyzer. Typical results indicated that the degradation rate increases with increasing applied voltage and decreases with increasing concentration. Dye degradation followed first order kinetics. The intermediate products formed during the degradation of MG were identified by a high resolution mass spectrometer (HR-MS) and proposed a plausible mechanism for the mineralization process.

Low-cost adsorbents from bio-waste for the removal of dyes from aqueous solution.

Activated carbons (ACs) were developed from bio-waste materials like rice husk and peanut shell (PS) by various physicochemical activation methods. PS char digested in nitric acid followed by treatment at 673 K resulted in high surface area up to ∼585 m(2)/g. The novelty of the present study is the identification of oxygen functional groups formed on the surface of activated carbons by infrared and X-ray photoelectron spectroscopy and quantification by using temperature programmed decomposition (TPD). Typical TPD data indicated that each activation method may lead to varying amounts of acidic and basic functional groups on the surface of the adsorbent, which may be a crucial factor in determining the adsorption capacity. It was shown that ACs developed during the present study are good adsorbents, especially for the removal of a model textile dye methylene blue (MB) from aqueous solution. As MB is a basic dye, H(2)O(2)-treated rice husk showed the best adsorption capacity, which is in agreement with the acidic groups present on the surface. Removal of the dye followed Langmuir isotherm model, whereas MB adsorption on ACs followed pseudo-second-order kinetics.

Abatement of mixture of volatile organic compounds (VOCs) in a catalytic non-thermal plasma reactor.

Total oxidation of mixture of dilute volatile organic compounds was carried out in a dielectric barrier discharge reactor with various transition metal oxide catalysts integrated in-plasma. The experimental results indicated the best removal efficiencies in the presence of metal oxide catalysts, especially MnO(x), whose activity was further improved with AgO(x) deposition. It was confirmed water vapor improves the efficiency of the plasma reactor, probably due to the formation of hydroxyl species, whereas, in situ decomposition of ozone on the catalyst surface may lead to nascent oxygen. It may be concluded that non-thermal plasma approach is beneficial for the removal of mixture of volatile organic compounds than individual VOCs, probably due to the formation of reactive intermediates like aldehydes, peroxides, etc.