Catalyst Recovery Research Articles

Copper adorned magnetic nanoparticles as a heterogeneous catalyst for Sonogashira coupling reaction in aqueous media

A nanomagnetic hydrophilic heterogeneous copper catalyst, termed γ-Fe2O3@PEG@PAMAM G0-Cu, has been successfully prepared and characterized using FT–IR, XRD, FE-SEM, TEM, EDX, mapping, TGA/DTG, VSM and ICP analyses. The catalyst displayed excellent activity for the palladium-free Sonogashira cross coupling reaction of various aryl iodides and bromides with phenylacetylene derivatives in pure water. The presence of polyethylene glycol coupled with hydrophilic character of the Cu-catalyst adorned on γ-Fe2O3 MNPs provides the ready dispersion of the catalyst particles in water, leading to higher catalytic performance as well as facile catalyst recovery via simple magnetic decantation. The recovered catalyst was reused for at least six successive runs with little reduction in its catalytic activity and any noticeable changes in its structure. The use of water as a green solvent, without requiring any additive or organic solvent, as well as the exploitation of abundant and low-cost copper catalyst instead of expensive Pd catalyst along with the catalyst recovery and scalability, make this method favorable from environmental and economic points of view for the Sonogashira coupling reaction.

Volatile potassium transfer behavior in carbon matrix and its effect on char gasification

Coal catalytic gasification is one of the effective ways to produce natural gas from coal. However, high cost and low recovery efficiency of catalyst increase the cost of catalytic gasification, which has become a restrictive factor for large-scale promotion of coal catalytic gasification. Therefore, the study on the migration behavior of potassium-based catalysts in the gasification process is of great significance for catalysts recovery. To understand the volatilization behavior between potassium and carbon matrix, the experiments were carried out in high temperature stage microscope (HTSM) and fixed-bed reactor. The migration of volatile potassium between particles was analyzed by SEM-EDS, while the chemical fraction of potassium species was determined by AAS, and the surface elements of the samples was investigated by XPS. The results showed that potassium would volatile at 765-770℃, C/K≈6.2–9.5(wt%), which would be adsorbed by the other char particles, leading to an increasing of the content of soluble potassium and ion-exchanged potassium, promoting carbon conversion in a limited effect and a decreasing of hydroxyl functional groups on the char particles. Meanwhile, the potassium content was proportional to the migration distance, the migration distance was about 720–800 μm at maximum under HTSM. The migration of potassium at high temperature caused the formation of liquid phase around the surface of char particles, which would prevent the contact between the gasifier agent and char particles and increase mass transfer resistance, thus preventing the increase of particle carbon conversion. In addition, no obvious liquid phase formation occurred at 800 °C in SFA-K, indicating that the formation of potassium-containing liquid phase and the volatilization of potassium at 800 °C were directly related to the carbon in the char.

Membrane-based TBADT recovery as a strategy to increase the sustainability of continuous-flow photocatalytic HAT transformations

Photocatalytic hydrogen atom transfer (HAT) processes have been the object of numerous studies showcasing the potential of the homogeneous photocatalyst tetrabutylammonium decatungstate (TBADT) for the functionalization of C(sp3)–H bonds. However, to translate these studies into large-scale industrial processes, careful considerations of catalyst loading, cost, and removal are required. This work presents organic solvent nanofiltration (OSN) as an answer to reduce TBADT consumption, increase its turnover number and lower its concentration in the product solution, thus enabling large-scale photocatalytic HAT-based transformations. The operating parameters for a suitable membrane for TBADT recovery in acetonitrile were optimized. Continuous photocatalytic C(sp3)-H alkylation and amination reactions were carried out with in-line TBADT recovery via two OSN steps. Promisingly, the observed product yields for the reactions with in-line catalyst recycling are comparable to those of reactions performed with pristine TBADT, therefore highlighting that not only catalyst recovery (>99%, TON > 8400) is a possibility, but also that it does not happen at the expense of reaction performance.

Insights into the performance and kinetics of face mask-derived nitrogen-doped porous carbon as peroxymonosulfate activator for gatifloxacin removal

The outbreak of COVID-19 has led to the increase in face mask waste globally. In this study, face mask-derived carbocatalysts doped with nitrogen (N-Mask) were fabricated through one-step pyrolysis of 1:5 w/w mixture of face mask and urea at different temperatures to activate peroxymonosulfate (PMS) for gatifloxacin (GAT) degradation. The N-Mask prepared at 800 °C (N-Mask800) exhibited the highest GAT degradation rate with kapp = 0.093 min−1 which could be attributed to its high N doping level (17.1 wt%) and highest specific surface area (237.13 m2 g−1). The relationship between kapp, catalyst loading and PMS dosage at various pHs on GAT degradation were successfully established. It was also found that the GAT degradation rate was inhibited in the sequential operating mode compared to the simultaneous operating mode. It was construed that adsorption and catalysis share the same active sites. Deterioration in catalytic performance was observed over successive cycles due to the surface chemistry change during catalysis, and difficulty in catalyst recovery after treatment. Radical scavenger study revealed that both radical and nonradical pathways were involved during GAT degradation, with nonradical pathway playing a dominant role. XPS analysis revealed that pyrrolic N and graphitic N can facilitate PMS activation via radical and nonradical pathways. Based on the LC-MS/MS analysis, the GAT degradation intermediates were identified, and the possible degradation pathways were tentatively proposed. Overall, this study demonstrated that carbocatalyst derived from face mask could be transformed into cost-effective and environmentally friendly PMS activator for environmental wastewater treatment applications.

Highly Chemoselective Catalytic Photooxidations by Using Solvent as a Sacrificial Electron Acceptor.

Catalyst recovery is an integral part of photoredox catalysis. It is often solved by adding another component-a sacrificial agent-whose role is to convert the catalyst back into its original oxidation state. However, an additive may cause a side reaction thus decreasing the selectivity and overall efficiency. Herein, we present a novel approach towards chemoselective photooxidation reactions based on suitable solvent-acetonitrile acting simultaneously as an electron acceptor for catalyst recovery, and on anaerobic conditions. This is allowed by the unique properties of the catalyst, 7,8-dimethoxy-3-methyl-5-phenyl-5-deazaflavinium chloride existing in both strongly oxidizing and reducing forms, whose strength is increased by excitation with visible light. Usefulness of this system is demonstrated in chemoselective dehydrogenations of 4-methoxy- and 4-chlorobenzyl alcohols to aldehydes without over-oxidation to benzoic acids achieving yields up to 70 %. 4-Substituted 1-phenylethanols were oxidized to ketones with yields 80-100 % and, moreover, with yields 31-98 % in the presence of benzylic methyl group, diphenylmethane or thioanisole which are readily oxidized in the presence of oxygen but these were untouched with our system. Mechanistic studies based on UV-Vis spectro-electrochemistry, EPR and time-resolved spectroscopy measurements showed that the process involving an electron release from an excited deazaflavin radical to acetonitrile under formation of solvated electron is crucial for the catalyst recovery.

Simultaneous hypercrosslinking and functionalization of polyHIPEs for use as coarse powder catalyst supports

Porous polymers offer desirable properties for heterogeneous catalysis, such as excellent stability, high active site density, and reusability. However, their synthesis is often complicated, requiring expensive reagents and laborious synthetic processes. We produce organophosphorus functionalized polyHIPEs by the polymerization of particle and surfactant stabilized water-in-styrene/divinylbenzene high internal phase emulsion templates, followed by post-functionalization using low-cost hypercrosslinking strategies. Three hypercrosslinking approaches were investigated, including knitting with an external crosslinker, solvent stitching and Scholl coupling reaction. Each approach’s ability to simultaneously create micro/mesoporosity and incorporate organophosphorus moieties into the polyHIPE structure as catalyst anchor sites were assessed, introducing surface areas of up to 410 m2/g and phosphorus concentrations of up to 7.4 wt%. After Pd-loading, the polyHIPEs displayed outstanding catalytic performance in a Suzuki-Miyaura coupling reaction, reaching turnover frequencies of 5722 h−1. The coarse powder form of the polyHIPEs allowed for simple catalyst recovery from the reaction mixture for reuse.

The insight into effects of oxygen vacancy on the activation of peroxymonosulfate via MOF-derived magnetic CoFe2O4 for degrading organic contaminants

Herein, MOF-derived magnetic CoFe2O4 with oxygen vacancy was successfully synthesized to activate peroxymonosulfate (PMS) for the effective degradation of emerging organic contaminants. The introduction of oxygen vacancy not only increased the specific surface area of CoFe2O4, but also reduce the charge transfer resistance. The CoFe2O4 with oxygen vacancy showed low charge transfer resistance and oxidation potential. Benefitting from the existence of oxygen vacancy, the PMS could be activated quickly by CoFe2O4 to produce SO4•−. As expected, developed CoFe2O4/PMS oxidation system displayed the excellent degradation ability toward various typical organic pollutants, and the organic pollutant could be mineralized into CO2, H2O and other inorganic molecules. Interestingly, both redox couples of Fe3+/Fe2+ and Co3+/Co2+ played a critical role in the PMS activation process. The SO4•−, OH•, O2•− and 1O2 were major active species in the CoFe2O4/PMS system, which were responsible for the degradation of organic pollutants. Furthermore, proposed CoFe2O4/PMS oxidation system also presented a wide pH range of applicability. The existence of magnetic property was convenient for the recovery of catalyst. All in all, this study provided a promising catalyst for the activation of PMS, and obtained results injected some new insights into the research on advanced oxidation processes (AOPs).

Ceramic nanofiltration membranes for efficient fouling mitigation through periodic electrolysis

Ceramic membranes are gaining importance in several mainstream membrane applications. Their high chemical and thermal resistance stability make them ideal candidates for oil/water separation, dye rejections, in dairy production, catalyst recovery and in treating a variety of wastewater effluents. Although ceramic microfiltration and ultrafiltration membranes are a predominant research area, there is still limited research on ceramic nanofiltration membranes, especially on controlling its fouling propensity. High flux values in such membranes can cause rapid fouling which lead to a compromise in membrane performance. In this work, we have modified commercial ceramic TiO2 NF membrane by coating it with titanium through an e-beam deposition process. Coating with titanium did not bring about any change in the inherent membrane properties such as its thermal resistance, structure and hydrophilicity. The superhydrophilic membrane showed good electrical conductivity, which enabled us to test the membrane for its self-cleaning ability through periodic electrolysis. Sodium alginate, yeast, humic acid and their mixtures were used as model foulants. A cross-flow filtration setup was used where the membrane acted as a cathode and a potential of 2–4.5 V was applied periodically depending upon the type of foulant. Without membrane cleaning, a sharp decline in flux to even till 10 % of its original value was noticed during some filtration tests. However, a high flux recovery from 88 to 98 % was achieved when the membrane was subjected to intermittent cleaning. The Ti-coated NF ceramic membrane showed efficient surface cleaning. The generation of hydrogen bubbles helped in sweeping away the cake layer formed as a result of concentration polarization. These electro-ceramic NF membranes allow us to address critical problems associated with such pressure driven processes where biofouling is a major problem.

The calcium alginate-immobilized Co-g-C3N4 composite microspheres as an efficient mediator to activate peroxymonosulfate for degrading organic pollutants

Poor water stability and difficult separation severely limited the application of Co-based catalysts in persulfate activation. Herein, for the first time, the calcium alginate-immobilized Co-g–C3N4–2 composite microspheres were prepared by a feasible method. Notably, embedding Co ion into g-C3N4 can improve its specific surface area and electrochemical activities. More significantly, as-prepared Co-g–C3N4–2 microsphere presented excellent catalytic performance in PMS activation for the degradation of TC. For the activation mechanisms of PMS over Co-g–C3N4–2 microspheres, the calcium alginate microspheres could mediate the direct electron transfer between TC and PMS, while both radical and nonradical pathways were involved in the activation of PMS over Co-g–C3N4–2. Meanwhile, SO4•−, OH•, O2•− and 1O2 were major reactive oxygen species formed in the Co-g–C3N4–2 microsphere/PMS system. Proposed Co-g–C3N4–2 microsphere/PMS system still exhibited great degradation ability towards TC over a wide pH range, and co-existing anions had weak influence on TC degradation over Co-g–C3N4–2 microsphere/PMS system. Moreover, the construction of Co-g–C3N4–2 microspheres not only avoided the release of metal ion from catalyst, but also provided convenience for the recovery of catalyst. In short, current work shared some novel insights into the application of heterogeneous catalysis in persulfate activation for wastewater treatment.

Copper‐amine complex immobilized on nano NaY zeolite as a recyclable nanocatalyst for the environmentally friendly synthesis of 2‐amino‐4H‐chromenes

The nano NaY zeolite‐supported copper‐amine complex was prepared by postmodification of the nano NaY zeolite with 3‐chloropropyl trimethoxysilane (CPTMS) and [2‐({3‐[(2‐aminoethyl)thio]propyl}thio)ethyl]amine followed by coordination with Cu (I) ion. Various techniques such as Fourier transform infrared spectroscopy (FT‐IR), X‐ray powder diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron micrograph (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), t‐plot, energy dispersive spectroscopy (EDS), inductively coupled plasma (ICP), and elemental analyses were used to characterize the structure of the synthesized catalyst. The catalytic activity of the synthesized nano‐sample was evaluated in a three‐component synthesis of 2‐amino‐4H‐chromene derivatives, which resulted in high reaction yields and short reaction times under green conditions. The catalyst is separated by filtration and can be reused for at least seven consecutive runs without significant loss of catalytic activity. The nature of the supported [2‐({3‐[(2‐aminoethyl)thio]propyl}thio)ethyl]amine (NN) on the zeolite's surface improved the catalytic activity of the zeolite, provided homogeneity to the catalyst, and enhanced the capability of coordination with copper ions. Facile catalyst recovery and reuse, simple setup procedure and generality of the method, high turnover number (TON), and aqueous ethanol as a green solvent make this procedure an environmentally benign approach for preparing the titled heterocycles. The findings in this work revealed that the introduced catalytic system could be used to prepare other beneficial heterocyclic compounds under environmentally benign conditions.

Hydrolysis of cellulose to fermentable sugars by using 2,5-furandicarboxylic acid as a recyclable catalyst in green solvent of GVL/ H2O

Hydrolysis of cellulose into C6 sugars is the starting point and entry point for biomass refining and is an important pathway for biofuel production. However, biomass-based 2,5-furandicarboxylic acid (FDCA) is a highly catalytic promising but underutilized organic carboxylic acid. In this paper, we investigated the use of easily recoverable FDCA as a catalyst for the hydrolysis of cellulose to produce C6 sugars in a γ-valerolactone/water (GVL/H2O) green solvent system. FDCA has high inherent acidity (pKa = 2.76) and stability with unique solubility in aqueous solutions and many solvents. These properties allows it to meet both high temperature solubility for efficient homogeneous hydrolysis reactions and low temperature crystallization catalysts for high purity recovery. This process not only solves the problem of solid-solid mass transfer between solid acid and cellulose which limits the hydrolysis rate, but also eliminates the problem of difficult separation and recovery of liquid acid catalysts. The results showed when initial concentration of microcrystalline cellulose was 0.7 wt%（equivalent to 7 g/L）, and the initial dosage of FDCA was 2.0 wt%, the maximum yield of C6 sugars reached 72.9% (40.1% glucose and 32.8% fructose) in GVL/H2O (60/40, V/V) with a reaction at 200 °C for 30 min. More importantly, FDCA can achieve 80% recovery and ＞99% spectroscopic purity recovery. This study reveals the potential of FDCA as a catalyst in the catalytic conversion of biomass, which provides a new pathway for the green and efficient conversion of biomass resources.

Ionic liquids enable highly efficient Knoevenagel reaction by dual-responsive emulsion microreactor

Knoevenagel condensation reaction is important for generating CC double bonds and providing various valuable intermediates in organic chemistry, which always need harsh conditions including high reaction temperature, difficult catalyst recovery, difficult product separation, etc. In this work, a novel class of dual-responsive emulsion reactor was prepared for the Knoevenagel condensation reaction between malononitrile and aromatic aldehyde, where the temperature and CO2-responsive ionic liquids (ILs) were used as an emulsifier, responder, and catalyst simultaneously. Driven by temperature or CO2, the emulsion reactor undergoes reversible and controllable transformations between emulsification and demulsification, where efficient catalytic reactions, product separation, and reactor recovery are all achieved. The isolated product yield of 2-(4-chlorobenzylidene)-malononitrile remained above 90% after 5 cycles of the emulsion reactor. NMR and molecular dynamics simulations showed that the temperature drives the reversible stretching and curling of the polyether chain on the cation, while CO2 reacts with the –COO- group on the anion to form carbonates and carboxylic acids in water, leading to changes in the surface activity of ILs, thereby reversibly regulating the demulsification and emulsification of the emulsion. Hence, through the dual stimuli-responsive ILs, the efficient reaction can be performed in the homogeneous phase, and the products and catalysts can be easily separated in the heterogeneous phase. These results on the revisable microreactor can not only help to design the smart and efficient “homogeneous reaction-heterogeneous separation” systems but also support the development of green sustainable chemistry.

Scalable and continuous access to pure cyclic polymers enabled by 'quarantined' heterogeneous catalysts.

Cyclic polymers are topologically interesting and envisioned as a lubricant material. However, scalable synthesis of pure cyclic polymers remains elusive. The most straightforward way is to recover a used catalyst after the synthesis of cyclic polymers and reuse it. Unfortunately, this is demanding because of the catalyst's vulnerability and inseparability from polymers, which reduce the practicality of the process. Here we develop a continuous circular process, where polymerization, polymer separation and catalyst recovery happen in situ, to dispense a pure cyclic polymer after bulk ring-expansion metathesis polymerization of cyclopentene. It is enabled by introducing silica-supported ruthenium catalysts and newly designed glassware. Different depolymerization kinetics of the cyclic polymer from its linear analogue are also discussed. This process minimizes manual labour, maximizes the security of vulnerable catalysts and guarantees the purity of cyclic polymers, thereby showcasing a prototype of a scalable access to cyclic polymers with increased turnovers (≥415,000) of precious catalysts.

Silver-anchored porous aromatic framework for efficient conversion of propargylic alcohols with CO2 at ambient pressure

The conversion of propargylic alcohols and carbon dioxide (CO2) into fine chemicals suffers from issues of harsh reaction conditions and difficult catalyst recovery. To achieve efficient CO2 activation at low energy consumption, a silver-anchored porous aromatic framework catalyst Ag@PAF-DAB with high active phase density and CO2 adsorption capacity was proposed. Since Ag@PAF-DAB has the dual functions of CO2 capture and conversion, propargylic alcohols were completely converted into α-alkylidene cyclic carbonate or α‑hydroxy ketone as high value-added product under atmospheric pressure (CO2, 0.1 MPa) and low silver equivalent (0.5 mol%). Notably, Ag@PAF-DAB exhibited broad substrate diversity, high stability, and excellent reusability. By applying FTIR and GC, the key to green synthetic route of α‑hydroxy ketone was confirmed to lie in the further hydration of α-alkylidene cyclic carbonate.

Central Composite Design of Biodiesel Production from Waste Cooking Oil using Tympanotonus fuscatus (Periwinkle) Shells as Catalyst

Biodiesel has been generally accepted as an environmentally – safer alternative to fossil based fuels. However, concerns of the cost of production, use of acid catalysts leading to corrosion, and recovery of homogenous catalyst remain. This study therefore seeks to optimize the transesterification process parameters in the conversion of waste cooking oil (WCO) using waste Tympanotonus fuscatus shell (WTFS). The catalysts were characterized using XRD, FTIR, and XRF. Temperatures ranging from 30°C to 90°C, catalyst loading from 1 to 10% by weight, and reaction durations from 30 to 180 minutes were examined for the transesterification technique. The physiochemical properties of the waste cooking oil revealed a high acid value (10.02mgKOH/g), kinematic viscosity of 13.30 mm2/s, pour point, 156oC, flash point of 104oC, Calorific value of 34.78 MJ/kg, carbon content of 2.65% m/m, among other parameters while the GCMS analysis indicated the presence of C16 to C21. The biodiesel however showed an acid value of 0.416 mgKOH/g, viscosity of 4.638 mm2/s, pour point of 0.3oC, flash point of 104oC, calorific value of 40.17 MJ/kg, and carbon content of 0.019% m/m which were in agreement with the EU and American standards. The elemental composition and crystalline structure of the catalyst revealed a considerable concentration of CaO, MgO, Al2O3, SiO2, and other metal oxides. The CCD approach used to design the experiments was significant (p <0.0001) and the biodiesel synthesis which resulted in a maximum yield of 91.70% was obtained with 5.5% WFTS, 105 minutes of reaction time, 65 oC, and a 1:7 oil–Methanol ratio. The operating parameters of temperature (p <0.0001), catalyst load (p = 0.00713), and time (p = 0.0288) all had significant effects on biodiesel yield; however, temperature had a stronger influence than the other process variables. The ANOVA results showed that the factors were extremely significant while Fit statistics and model comparison revealed a coefficient of determination of 97.66%, with the predicted value of 84.68% and the adjusted value of 95.00%. The biodiesel produced met the biodiesel standards.

A hierarchically porous and hygroscopic carbon-based catalyst from natural wood for efficient catalytic reduction of industrial high-concentration 4-nitrophenol

4-Nitrophenol (4-NP) with high toxicity and non-biodegradability has been causing a great threat to the environment and human health. Catalytic reduction of high-concentrated 4-NP in wastewater to 4-aminophenol (4-AP) and the subsequent recovery and reuse of catalysts are highly demanded for the practical treatment of industrial pollutants, yet are still limited in low mass transfer efficiency and poor stability of catalysts. Herein, we developed a composite catalyst of Pd nanoparticles (NPs) decorated 3D-activated carbon (Pd/3D-AC) to synergistically catalytic reduce high-concentrated industrial 4-NP (14.38 mM) by using natural wood as a 3D scaffold. The hierarchically porous 3D-AC demonstrates abundant surface-active sites (929 m2·g−1) for adequate and unaggregated anchoring Pd NPs (0.61 %), and the interconnected mass transfer channels and hygroscopic behavior of Pd/3D-AC yield an efficient chemical reaction in solution. As a result, the turnover frequency of the Pd/3D-AC is up to 1.68 min−1, and the synergistic interaction occurs to the 3D-AC and Pd NPs. Even after 10 cycles of catalysis, no deactivation was observed to Pd/3D-AC, demonstrating excellent stability and reusability. Moreover, the Pd/3D-AC catalyst contributes to a high conversion rate to 4-NP, with the yield of obtained 4-AP more than 99.9 % within 10 min. This facile strategy of loading metal nano-catalysts on hierarchically porous wood puts forward a flexible and effective approach for promoting the catalytic performance and the practical treatment of industrial wastewater.

Solid‐Supported Tetrahydropyran‐Based Hybrid Dipeptide Catalysts for Michael Addition of Aldehydes to Nitrostyrenes

AbstractThe heterogenization of homogeneous catalysts onto a solid support is a step towards a more sustainable chemistry. The recovery and reuse of catalysts is extremely important from a practical, economic and environmental point of view. In this regards, we report a series of polymer‐supported tetrahydropyran‐based hybrid dipeptides that serve as active catalysts for the enantioselective Michael addition of aldehydes to β‐nitrostyrenes. These supported catalysts have been designed considering the optimal anchor position and orientation between the catalyst and the solid support. Additionally, the influence of the linker length on the catalytic efficiency was studied. The catalysts allowed the transformation of a variety of substrates in 76–98% yield and with 94–97% enantiomeric excess. Detailed deactivation studies have provided important information, which allows to increase the useful life of these immobilized catalysts.magnified image

Heterostructured γ-Fe2O3/FeTiO3 magnetic nanocomposite: An efficient visible-light-driven photocatalyst for the degradation of organic dye

The catalyst recovery is the major concern in commercialization of photocatalysts for the industrial effluent treatment process. To overcome this major issue, Fe2O3 based magnetic photocatalytic heterostructure ɣ-Fe2O3/FeTiO3 nanocomposite was synthesized by hydrothermal method. Fe2O3 is the cheapest visible active magnetic photocatalytic material, but it has the limitation of fast e−/h + recombination. Titanium (Ti) was loaded on γ-Fe2O3 to overcome this issue. The loaded Ti has grown as FeTiO3 on the surface of ɣ-Fe2O3 nanocrystals and emerged as heterostructure ɣ- Fe2O3/FeTiO3 nanocomposites, which was confirmed by XRD and TEM results. The loading concentration of Ti on γ-Fe2O3 was optimized to achieve the maximum photocatalytic efficiency without compromising the magnetic property of γ-Fe2O3 to facilitate the magnetic separation. DRS-UV spectra revealed the strong visible light response of γ- Fe2O3/FeTiO3 nanocomposite. The photocatalytic efficiencies of the synthesized materials were evaluated using methylene blue (MB) as a model pollutant under sunlight. The built-in electric field between p-n junction between FeTiO3 and Fe2O3 and type II charge transfer mechanism extended the lifetime of the charge carriers at the heterojunction of γ- Fe2O3/FeTiO3, which was confirmed by PL spectra. The vibrating sample magnetometer (VSM) study revealed the decreasing magnetization, coercivity (Hc), and retentivity (Mr) of γ-Fe2O3 with increasing concentration of Ti. 92% of the used-up 20 wt% Ti loaded γ-Fe2O3/FeTiO3 magnetic nanocomposite was recovered from the treated wastewater using an electromagnet. Both magnetic properties and efficiency of the nanocomposite increased up to 20 wt% of Ti loading, beyond that decreased due to the increasing composition of antiferromagnetic FeTiO3 and the increasing number of defect sites as recombination centers. Hence, 20 wt% loading of Ti was concluded as the optimum to enhance the efficiency and to retain the magnetic properties. This work aims the commercialization of magnetic photocatalytic materials for the industrial effluent treatment.

Oligosaccharides as Green Catalyst for One-Pot Multicomponent Synthesis of Spirooxindole Derivatives in Water

A one pot synthetic methodology has been developed towards multicomponent synthesis of spiro[indoline-3,2'- quinazoline]-2,4'(3'H)-dione from isatoic anhydride, isatin and primary amines in aqueous medium via supramolecular catalysis. An untapped potential of β-Cyclodextrin to mediate multicomponent reactions in aqueous medium has been revealed. Developed protocol was further verified by extrapolating the synthetic protocol using different isatin derivatives and amine analogues. In other synthetic scheme, some compounds were synthesized by reaction of various substituted benzaldehydes, Isatoic anhydride and primary amines. Synthesized library of compounds were further characterized using various spectroscopic techniques. During all the synthetic process, the catalytic efficiency of cyclodextrin was exploited. Efficiency of all the three forms of cyclodextrins were tested to find the best reaction for synthesis of spiro compounds. The usefulness of β-cyclodextrin was proved by showing its reusability. The essential role of β-cyclodextrin in the synthetic methodology is further proved by doing the control experiments which showed that no product was formed in the absence of catalyst. The attachment of reactant molecule was also proved by doing 1H NMR of reaction mixture at different time interval in D2O. On the basis of observation, a plausible mechanistic pathway of reaction was proposed. Other two forms of cyclodextrins were also eliminated on the ground of their insuitability in the formation of desired product. Catalyst reusability was studied and it was shown that our catalytic system is useful without any significant loss in catalytic potential even after 5 cycles. Catalyst recovery procedure was established and was used without any significant loss of catalytic activity upto 5 times.

Carbon Dioxide Switchable Polymers – Recent Developments and Emerging Applications

AbstractCarbon dioxide has emerged as an alternative trigger for stimuli‐responsive or “switchable” materials that has unique advantages compared to conventional triggers. The principles of CO2 switching have been applied to a wide range of materials and processes, including polymeric materials and polymerization processes. This Perspective briefly reviews the types of polymer materials that have been made CO2‐switchable, and the types of processes where CO2 switching has been utilized to address process‐related challenges such as catalyst recovery. Recent research is then highlighted conducted in the groups on a range of new switchable polymers and processes, emphasizing emerging applications where CO2 switching may offer novel solutions and opportunities for commercial development.