CuNPs-loaded amines-functionalized-SBA-15 as effective catalysts for catalytic reduction of cationic and anionic dyes

In Situ Preparation of Silver Nanoparticles/Organophilic-Clay/Polyethylene Glycol Nanocomposites for the Reduction of Organic Pollutants

This work focuses on the preparation and application of silver nanoparticles/organophilic clay/polyethylene glycol for the catalytic reduction of the contaminants methylene blue (MB) and 4-nitrophenol (4-NP) in a simple and binary system. Algerian clay was subjected to a series of treatments including acid treatment, ion exchange with the surfactant hexadecyltrimethylammonium bromide (HTABr), immobilization of polyethylene glycol polymer, and finally dispersion of AgNPs. The molecular weight of polyethylene glycol was varied (100, 200, and 4000) to study its effect on the stabilization of silver nanoparticles (AgNPs) and the catalytic activity of the resulting samples. The results showed that the catalyst with the highest molecular weight of polyethylene glycol had the highest AgNP content. Catalyst mass, NaBH4 concentration, and type of catalyst were shown to have a significant influence on the conversion and rate constant. The material with the highest silver nanoparticle content was identified as the optimal catalyst for the reduction of both pollutants. The measured rate constants for the reduction of methylene blue (MB) and 4-nitrophenol (4-NP) were 164 × 10-4 s-1 and 25 × 10-4 s-1, respectively. The reduction of MB and 4-NP in the binary system showed high selectivity for MB dye, with rate constants of 64 × 10-4 s-1 and 9 × 10-4 s-1 for MB and 4-NP, respectively. The reuse of the best catalyst via MB dye reduction for four cycles showed good results without loss of performance.

Chitosan-sunflower meal biochar hydrogel incorporated with green synthesized NiO nanoparticles for enhanced catalytic reduction of anthropogenic water pollutants

Anthropogenic activities have been one of the crucial driving factors for water pollution globally, thereby warranting a sustainable strategy for its redressal. In this study, we have developed a hydrogel-biochar nanocomposite for catalytic reduction of water pollutants. To begin with, green synthesis of nickel oxide nanoparticles (NiO NPs) was accomplished from waste kinnow peel extract via the environmentally benign microwave method. The formation of NiO NPs was affirmed from different analytical techniques namely ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS). The FESEM images revealed spherical nature of NiO NPs. The average particle size was found to be 15.61 nm from XRD data. A novel hydrogel-biochar nanocomposite comprising the green NiO NPs, sunflower meal biochar and chitosan was prepared (Cs-biochar@ NiO) and explored as a nanocatalyst towards catalytic reduction of pollutants such as 4-nitrophenol, potassium hexacyanoferrate (III) and organic dyes methyl orange (MO), Congo red (CR), methylene blue (MB) in the presence of a reducing agent, i.e. NaBH4. Under optimized conditions, the reduction reactions were completed by 120 s and 60 s for 4-NP and potassium hexacyanoferrate (III) respectively and the rate constants were estimated to be 0.044 s-1 and 0.110 s-1. The rate of reduction was found to be faster for the dyes and the respective rate constants were 0.213 s-1 for MO, 0.213 s-1 for CR and 0.135 s-1 for MB. The assessment of the nanocatalyst in the reduction of binary dye systems depicted its selectivity towards the anionic dyes CR and MO. The nanocatalyst displayed effective reduction of dyes in real-water samples collected from different sources. Taken altogether, this study validates the design of sustainable hydrogel-biochar nanocatalyst for the efficient reduction of hazardous anthropogenic water pollutants.

Catalytic innovations: Improving wastewater treatment and hydrogen generation technologies

The effective reduction of hazardous organic pollutants in wastewater is a pressing global concern, necessitating the development of advanced treatment technologies. Pollutants such as nitrophenols and dyes, which pose significant risks to both human and aquatic health, making their reduction particularly crucial. Despite the existence of various methods to eliminate these pollutants, they are not without limitations. The utilization of nanomaterials as catalysts for chemical reduction exhibits a promising alternative owing to their distinguished catalytic activity and substantial surface area. For catalytically reducing the pollutants NaBH4 has been utilized as a useful source for it because it reduces the pollutants quiet efficiently and it also releases hydrogen gas as well which can be used as a source of energy. This paper provides a comprehensive review of recent research on different types of nanomaterials that function as catalysts to reduce organic pollutants and also generating hydrogen from NaBH4 methanolysis while also evaluating the positive and negative aspects of nanocatalyst. Additionally, this paper examines the features effecting the process and the mechanism of catalysis. The comparison of different catalysts is based on size of catalyst, reaction time, rate of reaction, hydrogen generation rate, activation energy, and durability. The information obtained from this paper can be used to steer the development of new catalysts for reducing organic pollutants and generation hydrogen by NaBH4 methanolysis.

Zinc nanoparticles encapsulated in porous biopolymer beads for reduction of water pollutants and antimicrobial activity

This work focuses on the preparation of composite beads from alginate crosslinked with copper at several loading percent and also loaded with ZnNPs. Th obtained samples were applied as catalysts for the reduction of the organic polluants 4-NP, MB, OG, MO, and CR in simple and binary systems. XRD results and TEM images confirmed the presence of ZnNPs in the polymer matrix. XRF and TGA analysis showed that the percentage of the cross-linking agent significantly influences the content of ZnNPs as well as the thermal stability of the resulting material. The catalytic activity of the composite beads showed that the Cu(4 %)-ALG(ZnNPs) sample was the best catalyst for all pollutants. In the simple system, the recorded rate constants for MB, MO, 4-NP, OG, and CR were 0.0133 s-1, 0.0076 s-1, 0.005 s-1, 0.0042 s-1, 0.0036 s-1, respectively. The catalyst was more selective towards the cationic MB dye for binary systems. For antibacterial and antifungal applications, the different materials containing ZnNPs and their counterparts containing Zn2+ were found to be active across all bacterial strains (Gram positive and Gram negative) as well as fungi, and the Zn2+-containing composites in particular performed better across all bacteria and fungi.

Elimination of toxic azo dye using a calcium alginate beads impregnated with NiO/activated carbon: Preparation, characterization and RSM optimization

Nickel oxide nanoparticles supported activated carbon (AC-NiO) was fabricated using thermal activation. Then, AC-NiO composite was immobilized on alginate beads to obtain 3-dimensional network structure ALG@AC-NiO nanocomposite beads for catalytic reduction of Congo red (CR) dye. The resulting nanocomposite beads were identified by various physical techniques. The crystalline nature and dispersion of NiO nanoparticles was defined by the XRD and EDS techniques, respectively. ALG@AC-NiO beads have a Ni element content of 4.65 wt% with an average NiO particle diameter of 23 nm. The statistical approach mathematically describes the catalytic reduction of the CR dye as a function of the NaBH₄ concentration, the catalyst dose and the concentration of the CR dye modeled by a BBD-RSM. According to the statistical modeling and the optimization process, the catalytic optimum conditions were obtained for NaBH₄ concentration of 0.05 M, catalyst dose of 11 mg and CR dye concentration of 80 ppm who permit meet 99.67 % of CR dye conversion. The adjusted coefficient of determination (R² = 0.9957) indicates that the considered model was quite suitable with a good correlation between the experiment and predicted.

Catalytic reduction of organic pollutants, antibacterial and antifungal activities of AgNPs@CuO nanoparticles-loaded mesoporous silica

In this work, the mesoporous silica MCM-41 was prepared by a hydrothermal method and then modified using silver and copper. The obtained samples were used as antibacterial/antifungal agents and as catalysts for the reduction of the following dyes: Methylene Blue (MB), Congo Red (CR), Methyl Orange (MO), and Orange G (OG). Several parameters affecting the reduction of dyes were investigated and discussed such as the catalyst nature, the initial concentration of the dye, the dye nature, the selectivity of the catalyst in a binary system as well as the catalyst reuse. The catalysts were characterized using XRD, nitrogen sorption measurements, XRF, FTIR, XPS, SEM/EDS, and TEM. XRD, XPS, and TEM analysis clearly showed that the calcination of copper- and silver-modified silica leads to the formation of well-dispersed CuO and AgNPs having sizes between 5 and 10 nm. As determined by XRF analysis, the content of silver nanoparticles was higher compared to CuO in all samples. It has been shown that the dye reduction is influenced by the size and the content of nanoparticles as well as by their dispersions. The catalytic activity was shown to be the highest for the Ag-Cu-MCM(0.05) catalyst with a rate constant of 0.114, 0.102, 0.093, and 0.056 s^-1 for MO, MB, CR, and OG dyes in the single-dye system, respectively. In the binary system containing MB/OG or MB/MO, the catalyst Ag-Cu-MCM(0.05) was more selective toward the MB dye. The reuse of the catalyst for three consecutive cycles showed higher MB conversion in a single system with an increase in reaction time. For antifungal and antibacterial properties, the application of calcined and uncalcined materials toward six different strains showed good results, but uncalcined materials showed the best results due to the synergistic effect between CuO and unreduced species Ag⁺ which are considered responsible for the antibacterial and antifungal action.

Organoselenium functionalized SBA-15 as a new catalyst for the cyanide-free conversion of oximes to nitriles

BACKGROUND

Here we report a new selenium-based heterogeneous catalyst, which was prepared from the immobilization of diphenyl diselenide on amine-functionalized Santa Barbara Amorphous-15 (SBA-15). The catalyst characterization study has been confirmed by different analysis methods including Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction patterns (XRD), field-emission scanning electron microscopy (FE-SEM), and Brunauer-Emmett-Teller (BET) surface area analysis.

RESULTS

The newly designed catalyst was successfully applied in the green dehydration reaction of oximes to corresponding nitriles in the presence of hydrogen peroxide/air. To demonstrate the role of the catalyst in this study, the model reaction was also carried out in the absence of the catalyst and a trace yield of the relevant product was achieved.

CONCLUSION

In this way, a series of nitrile derivatives were obtained with 72-96% yields, also, the catalyst could be separated easily and recycled for four consecutive runs with no obvious drop in catalytic activity.

Catalytic Reduction of Dyes and Antibacterial Activity of AgNPs@Zn@Alginate Composite Aerogel Beads

This work focuses on the preparation of aerogel composite beads based on Zn(II)-crosslinked alginate and loaded with different percentages of AgNPs using a simple approach. The obtained samples were evaluated in two different applications: the first application consists in their use as catalysts for the reduction of MB, MO, OG and CR dyes in a simple and binary system under the presence of NaBH₄. For this, several parameters affecting the catalytic behavior of these catalysts have been investigated and discussed such as the catalyst mass, AgNPs content, dye nature, and the selectivity of the catalyst in a binary system. The second application concerns their antibacterial activities towards two Gram-negative bacteria Escherichia coli (ATCC 25922), and Pseudomonas aeruginosa (ATCC 27853), and a Gram-positive bacteria Staphylococcus aureus (ATCC 25923). The physico-chemical properties of different samples were characterized by XRD, FTIR, SEM/EDS, and TGA analysis. The obtained results confirmed the presence of AgNPs on a highly porous alginate structure. The dispersion of a high percentage of AgNPs leads to the formation of nanoparticles on the outer surface of the alginate which led to their leaching after the catalytic test, while the composite having a low percentage of AgNPs showed good results through all dyes without leaching of AgNPs. For the antibacterial application of the different samples, it was shown that a composite with a higher percentage of AgNPs was the most effective against all bacteria.

Core-shell alginate beads as green reactor to synthesize grafted composite beads to efficiently boost single/co-adsorption of dyes and Pb(II)

A series of sodium alginate (SA) grafted polymer composite beads were synthesized by a solution free-radical graft polymerization reaction performed in a surface crosslinked alginate bead reactor. The outer surface of the precursor droplet containing reactants including SA, acrylamide (AM), N,N'-methylene-bis-acrylamide (MBA), ammonium persulfate (APS), sepiolite (SP) and gelatin (GE) was instantly crosslinked with Ca²⁺ ions to form a capsule-like bead when it was dropped into aqueous solution of calcium chloride, and simultaneously the reactants inside the capsule-like "bead reactor" were polymerized in-situ to form new composite beads with crosslinked network structure, abundant functional groups, single or co-adsorption ability and easily separable advantages. The optimal composite bead shows high adsorption capacity of 390.78, 1425.65 and 533.91 mg/g towards Methylene Blue (MB), Basic Fuchsin (BF) and Pb(II), respectively. After adsorption by the composite bead, 99.71% of MB, 99.99% of BF and 99.97% of Pb(II) were removed from original dye or Pb(II) solutions. Moreover, above 99.22% of BF and 95.33% of Pb(II) was co-removed from their binary mixture (BF concentration, 100 mg/L; Pb(II) concentration, 50 mg/L). This paper provides a simple green way to synthesize efficient and recyclable biopolymer-based adsorbents capable of purifying dyes and heavy metal ions in water.

Catalytic behavior and antibacterial/antifungal activities of new MNPs/zeolite@alginate composite beads

In this paper, a new family of composite materials was prepared based on calcium alginate and metal nanoparticle-loaded zeolite omega. Different types of metal nanoparticles (MNPs), namely Cu, Co and Fe, were loaded onto zeolite omega to test the performance of the resulting metal/zeolite@alginate composites towards the catalytic reduction of methylene blue dye. To examine their application field as broadly as possible, these composite beads were also tested as antibacterial and antifungal agents against several types of bacteria. Several techniques such as XRD, XRF, FTIR, XPS, SEM and TGA were used to characterize the samples. The obtained results showed that all the composite bead samples were effective in the reduction of MB dye. The composite Co/Zeolite@ALG with relatively low Co nanoparticle (NP) content was selected as the best performing catalyst due to its reduction of MB dye being completely achieved in 3 min with a rate constant of 1.4 min-1, which was attributed to its highly porous structure. The reuse tests conducted on the best-performing catalyst showed good results which persisted through five successive cycles. For antibacterial and antifungal activities, the Cu/Zeolite@ALG and Fe/Zeolite@ALG composites showed good activity with significant inhibition zones.