Microwave assisted catalytic oxidation of p-nitrophenol in aqueous solution using carbon-supported copper catalyst

Efficient phenolic compounds adsorption by immobilization of copper-based metal-organic framework anchored polyacrylonitrile/chitosan beads

The application of newly formulated beads from copper-benzenetricarboxylate (Cu-BTC), polyacrylonitrile (PAN), and chitosan (C), Cu-BTC@C-PAN, C-PAN, and PAN, for the removal of phenolic chemicals from water, is described in the current paper. Phenolic compounds (4-chlorophenol (4-CP) and 4-nitrophenol (4-NP)) were adsorbed using beads and the adsorption optimization looked at the effects of several experimental factors. The Langmuir and Freundlich models were used to explain the adsorption isotherms in the system. A pseudo-first and second-order equation is performed for describing the kinetics of adsorption. The obtained data fit (R² = 0.999) supports the suitability of the Langmuir model and pseudo-second-order kinetic equation for the adsorption mechanism. Cu-BTC@C-PAN, C-PAN, and PAN beads' morphology and structure were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transforms infrared spectroscopy (FT-IR). According to the findings, Cu-BTC@C-PAN has very high adsorption capacities of 277.02, and 324.74 mg g^-1, for 4-CP and 4-NP, respectively. The Cu-BTC@C-PAN beads showed 2.55 times higher adsorption capacity than PAN in the case of 4-NP, but in the case of 4-CP, it was higher by 2.64 times.

Copper-based MOF, Cu3(SDBA)2(HSDBA), as a catalyst for efficient reduction of 4-nitrophenol in the presence of sodium borohydride

Herein, we report the synthesis of the copper-based MOF, Cu3(SDBA)2(HSDBA), using a solvothermal method.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Biogenic Synthesis of Gold Nanoparticles on a Green Support as a Reusable Catalyst for the Hydrogenation of Nitroarene and Quinoline

Direct attachment of gold nanoparticles to a green support without the use of an external reducing agent and using it for removing toxic pollutants from wastewater, i. e., reduction of nitroarene to amine, are described. A novel approach involving the reduction of gold by the jute plant (Corchorus genus) stem-based (JPS) support itself to form nanoparticles (AuNPs) to be used as a catalytic system ('dip-catalyst') and its catalytic activity for the hydrogenation of series of nitroarenes in aqueous media are presented. AuNPs/JPS catalyst was characterized using SEM, UV-Vis, FTIR, TEM, XPS, and ICP-OES. Confined area elemental mapping exhibits uniform and homogeneous distribution of AuNPs on the support surface. TEM shows multi-faceted AuNPs in the range of 20-30 nm. The reactivity of AuNPs/JPS for the transfer hydrogenation of nitroarene as well as hydrogenation of quinoline under molecular H₂ pressure was evaluated. Sodium borohydride, when used as the hydrogen source, demonstrates a high catalytic efficiency in the transfer hydrogenation reduction of 4-nitrophenol (4-NP). Quinoline is quantitatively and chemoselectively hydrogenated to 1,2,3,4-tetrahydroquinoline (py-THQ) using molecular hydrogen. Reusability studies show that AuNPs are stable on the support surface and their selectivity is not affected.

Ranolazine-functionalized CuO NPs: efficient homogeneous and heterogeneous catalysts for reduction of 4-nitrophenol

In the present study copper oxide nanoparticles (CuO NPs) were synthesized using a hydrothermal method with ranolazine as a shape-directing agent. Ranolazine-functionalized CuO NPs were characterized by various analytical techniques such as scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The SEM pattern confirmed the morphology of ranolazine-functionalized CuO NPs with well-defined rice-like structures. FTIR spectroscopy confirmed the interaction between CuO NPs and ranolazine. The XRD analysis indicated that the structure of ranolazine-functionalized CuO NPs was monoclinic crystalline and the size ranged between 9 and 18 nm with an average particle size of 12 nm. The smaller size range of CuO NPs gave a large surface area that enhanced the efficiency of these catalysts employed for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the H ₂ O system. In homogeneous catalysis, results showed that 50 μL of CuO NPs was required in the presence of NaBH4 for 99% reduction of 4-NP in 240 s. On the other hand, for heterogeneous catalysis, 0.5 mg of CuO NPs was used in the presence of NaBH4 for 99% catalytic reduction of 4-NP to 4-AP in 320 s. The rate of reaction for homogeneous catalysis and heterogeneous catalysis was determined from the plots of In(Ct /C0) of 4-NP versus time (s), which showed good linearity with values of 1.3 × 10 ^-2 and 8.8 × 10 ^-3 s ^-1 . respectively. The high-quality catalytic efficiency, good reusability, nontoxic nature, and low cost are favorable properties of the synthesized CuO NPs for use as efficient catalysts for reduction of 4-AP to 4-NP in both homogeneous and heterogeneous media.

Copper hexacyanoferrate nanocrystal as a highly efficient non-noble metal catalyst for reduction of 4-nitrophenol in water

As Prussian Blue analogues (PBAs) represent one of the most classical families of coordination compounds and exhibit versatile catalytic activities, PBAs have been considered as useful heterogeneous catalysts for reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Nevertheless, while Cu has been a well-proven transition metal for 4-NP reduction, especially, due to their ability to attain pronounced conversions of reactants under mild conditions, environmental friendliness and great stability. Nevertheless, while Cu has been a well-proven transition metal for 4-NP reduction, Cu-based PBA has never been developed and thoroughly investigated for 4-NP reduction. Thus, in this study, copper hexacyanoferrate, Cu^II₃[Fe(CN)₆]₂ (CuFeCN) is particularly synthesized and proposed for the first time as a catalyst for reduction of 4-NP in the presence of NaBH₄. CuFeCN exhibits a very high catalytic activity towards reduction of 4-NP to 4-AP with 100% conversion within 4 min. The activity factor (AF) at room temperature, 8057.14 s^-1 g^-1, is between 1 and 2 orders higher than all other MFeCN Prussian blue analogues (M = Co, Fe, Ni, Zn, and Mn). In addition, CuFeCN shows excellent reusability to achieve 100% conversion of 4-NP to 4-AP with highly stable rate constants over successive 7 cycles. The activation energy (E_a) and turn over frequency (TOF) for the reduction of 4-NP to 4-AP catalyzed by CuFeCN system are determined as 24.6 kJ mol^-1 and 36.93 min^-1, respectively, which are both significantly more superior than most of reported catalysts in literatures. These advantageous properties make CuFeCN ideal to be developed into a promising catalyst for elimination of nitroaromatic contaminants in water.

Acoustic cavitation assisted destratified clay tactoid reinforced in situ elastomer-mimetic semi-IPN hydrogel for catalytic and bactericidal application

Ultrasonicaion is non-chemical process where acoustic waves have been targeted to aqueous medium dispersed precursor materials. In situ synthesis of silver nanoparticles anchored in hydrogel matrix has been opted via ~20 kHz frequency assisted (bath sonication) synthesis having the ultrasonication power intensity (UPI) of ~10⁶ J/m². Power intensity is inversely proportional to the surface area of the clay tactoids. The hydrogel have been prepared by in situ 20 kHz assisted sonochemical destratification of laponite clay tactoids which could be terminologically stated as 'top-down method'. Silver nanoparticles (AgNPs) have been deposited in the surfaces of the porous matrix of hydrogel via 'soak and irradiate' method. Soaking of silver ions into the gel matrix is welcomed due to their efficient stabilization and fast transformation towards AgNPs. AgNPs played the key role in catalytic reduction and bactericidal activity. Moreover, the prepared hydrogel has enough robust to withstand cyclic stress, uniaxial stress and oscillatory stress which have been extensively justified by the physico-mechanical characterizations. The gel supported catalyst showed first order reaction kinetics and less time consuming period during reduction of 4-nitrophenol as a model pollutant.

Microwave irradiation directly excites semiconductor catalyst to produce electric current or electron-holes pairs

Generally, photon of Microwave (MW) electromagnetic waves have long been thought to be lower energy, which could not excite metals or semiconductor materials to generate electric current and electron-holes pairs (e⁻_cb + h⁺_vb). In this paper, we report an unexpected, Microwave “photoelectric effect”, when MW irradiates on the semiconductor materials, leading to generate electric current and electron-holes pairs (e⁻_cb + h⁺_vb), on the semiconductor materials and on the MW catalyst. Further, we show that the action mechanism of Microwave “photoelectric effect” made water adsorbing on the surface of Microwave catalyst transform into hydroxyl radical (∙OH). Thus, this study has revealed the principle of generation Microwave “photoelectric effect” under MW irradiation, and the mechanism of MW catalytic oxidation degradation of organic in the wastewater and the mechanism of MW reduction method for preparation of nano-particle metal supported catalysts. Our findings challenge the classic view of MW irradiation only as heating method, which cannot excite to produce electric current and electron-holes pairs (e⁻_cb + h⁺_vb). Our findings will open new field to use MW technology for MW catalytic oxidation degradation of organics in the wastewater, and for MW reduction method of metal supported catalysts preparation.

Synthesis of Silver Nanoparticles Loaded onto Polymer-Inorganic Composite Materials and Their Regulated Catalytic Activity

We present a novel approach for the preparation of polymer-TiO₂ composite microgels. These microgels were prepared by the in situ hydrolysis and condensation of titanium tetrabutoxide (TBOT) in a mixed ethanol/acetonitrile solvent system, using poly(styrene-co-N-isopropylacrylamide)/poly(N-isopropylacrylamide-co-methacrylic acid) (P(St-NIPAM/P(NIPAM-co-MAA)) as the core component. Silver nanoparticles (AgNPs) were controllably loaded onto the polymer-TiO₂ composite microgels through the reduction of an ammoniacal silver solution in ethanol catalyzed by NaOH. The results showed that the P(St-NIPAM)/P(NIPAM-co-MAA)-TiO₂ (polymer-TiO₂) organic-inorganic composite microgels were less thermally sensitive than the polymer gels themselves, owing to rigid O–Ti–O chains introduced into the three-dimensional framework of the polymer microgels. The sizes of the AgNPs and their loading amount were controlled by adjusting the initial concentration of [Ag(NH₃)₂]⁺. The surface plasmon resonance (SPR) band of the P(St-NIPAM)/P(NIPAM-co-MAA)-TiO₂/Ag (polymer-TiO₂/Ag) composite microgels can be tuned by changing the temperature of the environment. The catalytic activities of the polymer-TiO₂/Ag composite microgels were investigated in the NaBH₄ reduction of 4-nitrophenol. It was demonstrated that the organic-inorganic network chains of the polymer microgels not only favor the mass transfer of the reactant but can also modulate the catalytic activities of the AgNPs by tuning the temperature.

Rapid degradation of malachite green by CoFe2O4-SiC foam under microwave radiation

This study demonstrated rapid degradation of malachite green (MG) by a microwave (MW)-induced enhanced catalytic process with CoFe₂O₄-SiC foam. The catalyst was synthesized from CoFe₂O₄ particles and SiC foam by the hydrothermal method. X-ray diffraction and scanning electron microscopy techniques were used to confirm that CoFe₂O₄ particles were settled on the surface of SiC foam. In this experiment, a novel fixed-bed reactor was set up with this catalyst for a continuous flow process in a MW oven. The different parameters that affect the MW-induced degradation rate of MG were explored. The MW irradiation leads to the effective catalytic degradation of MG, achieving 95.01% degradation within 5 min at pH 8.5. At the same time, the good stability and applicability of CoFe₂O₄-SiC foam for the degradation process were also discussed, as well as the underlying mechanism. In brief, these findings make the CoFe₂O₄-SiC foam an excellent catalyst that could be used in practical rapid degradation of MG.

Pyrochlore Ce2Zr2O7 decorated over rGO: a photocatalyst that proves to be efficient towards the reduction of 4-nitrophenol and degradation of ciprofloxacin under visible light

The synergistic interaction between phase pure Ce₂Zr₂O₇ and rGO enhances the photoreduction of 4-nitrophenol under visible light.

Highly efficient degradation of 4-nitrophenol over the catalyst of Mn2O3/AC by microwave catalytic oxidation degradation method

A new microwave catalytic oxidation process based on two kinds of catalysts, the commercially available activated carbon (AC) and Mn2O3 nanoparticle modified AC (Mn2O3/AC), was reported for the degradation of 4-nitrophenol (4-NP) without adding any oxidant. Effects of microwave power, catalyst dosage, irradiation time, and initial concentration for the degradation efficiency were studied. Results indicated that catalyst of Mn2O3/AC showed much higher catalytic activity than pure AC and Mn2O3 particles. Significantly, 4-NP degradation efficiency reached 99.6%, corresponding to 93.5% TOC removal under optimal conditions with microwave power of 400W, Mn2O3/AC dosage of 2g, reaction time of 5min, and initial concentration of 100mg/L. Hydroxyl radicals (OH) generated during catalytic reaction is the main oxidant, and O2 can not effectively improve removal rate. We proposed the microwave 'photoelectric effect' to interpret the generation of OH in view that microwave irradiation can directly excite the catalyst to produce electron-hole pairs and then transform H2O into OH on the surface of catalyst in solution. The obtained kinetic equation for microwave catalytic oxidation degradation of 4-NP was in line with pseudo-first-order kinetic model, that is, apparent rate constant increased as microwave power density increase.

Self-assembled material of palladium nanoparticles and a thiacalix[4]arene Cd(ii) complex as an efficient catalyst for nitro-phenol reduction

A cadmium complex based on the thiacalix[4]arene scaffold is utilized to synthesize a material with palladium nanoparticles, which behaves as an efficient catalyst for the conversion of 4-nitrophenol to 4-aminophenol.

High surface area and oxygen-enriched activated carbon synthesized from animal cellulose and evaluated in electric double-layer capacitors

Mechanism diagram for the synthesis of activated carbons from crab shell wastes.

Phoenix dactylifera L. leaf extract phytosynthesized gold nanoparticles; controlled synthesis and catalytic activity

A green synthesis route was reported to explore the reducing and capping potential of Phoenix dactylifera extract for the synthesis of gold nanoparticles. The processes of nucleation and growth of gold nanoparticles were followed by monitoring the absorption spectra during the reaction. The size and morphology of these nanoparticles was typically imaged using transmission electron microscopy (TEM). The particle size ranged between 32 and 45 nm and are spherical in shape. Fourier transform infrared (FTIR) analysis suggests that the synthesized gold nanoparticles might be stabilized through the interactions of hydroxyl and carbonyl groups in the carbohydrates, flavonoids, tannins and phenolic acids present in P. dactylifera. The as-synthesized Au colloids exhibited good catalytic activity for the degradation of 4-nitrophenol.

Spontaneous synthesis of gold nanoparticles on gum arabic-modified iron oxide nanoparticles as a magnetically recoverable nanocatalyst

A novel magnetically recoverable Au nanocatalyst was fabricated by spontaneous green synthesis of Au nanoparticles on the surface of gum arabic-modified Fe3O4 nanoparticles. A layer of Au nanoparticles with thickness of about 2 nm was deposited on the surface of gum arabic-modified Fe3O4 nanoparticles, because gum arabic acted as a reducing agent and a stabilizing agent simultaneously. The resultant magnetically recoverable Au nanocatalyst exhibited good catalytic activity for the reduction of 4-nitrophenol with sodium borohydride. The rate constants evaluated in terms of pseudo-first-order kinetic model increased with increase in the amount of Au nanocatalyst or decrease in the initial concentration of 4-nitrophenol. The kinetic data suggested that this catalytic reaction was diffusion-controlled, owing to the presence of gum arabic layer. In addition, this nanocatalyst exhibited good stability. Its activity had no significant decrease after five recycles. This work is useful for the development and application of magnetically recoverable Au nanocatalyst on the basis of green chemistry principles.

Facile, template-free synthesis of silver nanodendrites with high catalytic activity for the reduction of p-nitrophenol

Here we report a facile, surfactant-free and template-free synthesis process of highly uniform dendritic silver nanostructures with high catalytic activity for the reduction of p-nitrophenol. By controlling the concentration of AgNO(3) aqueous solution and the reaction time, various shapes of silver nanodendrites (SNDs) could be obtained easily. The effects of different parameters such as concentrations of the reagents and reaction time on the morphology and structure of as-prepared tree-like nanostructures have also been investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Also, the X-ray photoelectron spectroscopy (XPS) has been used to identify the oxidation state of SNDs. In addition, the catalytic activity of the as-prepared SNDs samples at 200 mM AgNO(3) aqueous solution was evaluated by a redox reaction of p-nitrophenol in the presence of an excess amount of NaBH(4). It was found that the highly symmetrical SNDs with roughly 60-120 nm in stem and branch diameter and 3-12 μm in length obtained after 120 s reaction time do have higher catalytic activity than other SNDs prepared at different reaction time, several times stronger catalytic activity in the sodium borohydride reduction of p-nitrophenol to p-aminophenol, compared to some other silver nanoparticles reported in literature. The crystallinity provided by X-ray diffraction (XRD) analysis indicates that the improvement of the crystallinity is also very crucial for SNDs' catalytic activities. The SNDs are very promising catalytic candidates for the reduction of p-nitrophenol because of easily simple preparation route and high catalytic activity.