A Visible Light-Driven α-MnO2/UiO-66-NH2 S-Scheme Photocatalyst toward Ameliorated Oxy-TCH Degradation and H2 Evolution

Photocatalytic hydrogen production and pollutant degradation using a heterogeneous photocatalyst remains an alternative route for mitigating the impending pollution and energy crisis. Hence, the development of cost-effective and environmentally friendly semiconducting materials with high solar light captivation nature is imperative. To overcome this challenge, α-MnO2 nanorod (NR)-modified MOF UiO-66-NH2 (UNH) was prepared via a facile solvothermal method, which is efficient toward H2 evolution and oxy-tetracycline hydrochloride (O-TCH) degradation. The field-emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HR-TEM) results of the α-MnO2@UNH (MnU) hybrid reveals its nanorod embedded in MOF matrix, and the X-ray photoelectron spectroscopy (XPS) result confirms the interaction of UNH moiety with α-MnO2 NRs. Additionally, the outstanding separation of photogenerated excitons and the charge-transfer efficacy are further validated by photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical impedance spectroscopy (EIS), and transient photocurrent analysis, which are the key causes for photoactivity augmentation in the MnU composites. The MnU-2 composite shows a superior O-TCH degradation efficiency of 93.23% and an excellent H2 production rate of about 410.6 μmol h-1 upon light irradiation. This study provides significant evidence in favor of the suggested mediator-free S-scheme-adapted charge migration path, and it effectively explains the enhanced exciton separation leading to extraordinary catalytic efficiency of the proposed composite.

Green synthesis of MnO2 nanoparticles from Psidium guajava leaf extract: Morphological characterization, photocatalytic and DNA/BSA interaction studies

In this work, a simple, efficient and eco-friendly green synthesis of manganese dioxide nanoparticles (MnO2NPs) by Psidium guajava leaf extract was described. Fourier-Transform infrared spectra results revealed that involvement of the plant extract functional groups in the formation of MnO2NPs. The UV-vis absorption spectra of the synthesized MnO2NPs exhibited absorption peaks at 374 nm, which were attributed to the band gap of the MnO2NPs. Crystal phase identification of the MnO2NPs were characterized by X-ray diffraction analysis and the formation of crystalline MnO2NPs have been confirmed. Furthermore, scanning electron microscopy analysis showed that the synthesized MnO2NPs have a spherical in shape. Interestingly, the prepared green synthesized MnO2NPs showed catalytic degradation activity for malachite green dye. Malachite green's photocatalytic degradation was detected spectrophotometrically in the wavelength range of 250-900 nm, and it was discovered to have a photodegradation efficiency of 75.5 % within 90 min when exposed to solar radiation. Green synthesized MnO2NPs are responsible for this higher activity. An interaction between synthesized NPs and biomolecules, including CT-DNA and BSA was also evaluated. The spectrophotometric and Fluoro spectroscopic analyses indicate a gradual reduction in peak intensities and shifts in wavelengths, indicating binding and affinity between the NPs and the biomolecules.

Chitosan grafted polyacrylic acid doped MnO2 nanocomposite an efficient dye degrader and antimicrobial agent

Manganese dioxide (MnO2) nanorods and (3, 6, and 9 mL) chitosan grafted polyacrylic acid (CS-g-PAA) doped MnO2 were prepared hydrothermally. The study objective is to decrease the recombination rate of MnO2 upon doping to enhance the dye degradation efficiency and antimicrobial activity. The doping-dependent properties of CS-g-PAA on phase identification, functional groups, optical characteristics, elemental compositions, and morphological analyses of MnO2 nanorods were conducted using systematic characterization techniques. XRD pattern shows that MnO2 has a tetragonal structure, with increased crystallite size (15.87 to 29.36 nm) upon doping. The TEM analysis showed that MnO2 has nanorods and that CS-g-PAA doped MnO2 displayed nanoflakes-like structures. The decrease in electron-hole pair recombination rate on doping was verified by PL spectroscopy, demonstrating the enhanced catalytic activity. Moreover, adding grafted binary polymers to MnO2 inhibits bacterial cell growth by binding with the negatively charged cell wall and preventing biofilm formation. The 9 mL doped sample displayed a maximum degradation (99.27 %) in a neutral medium and 85.84 % antimicrobial efficiency against E. coli. The enoyl-acyl carrier protein reductase (FabIE. coli) and DNA gyrase(E. coli) were inhibited by these CS-g-PAA doped MnO2 nanostructures (NSs), as shown by in silico molecular docking studies.

Comprehensive evaluation of cobalt incorporated cryptomelane-type manganese oxide molecular sieve as an efficient adsorbent for enhanced removal of europium from wastewater systems

Extraction of radionuclide contaminants from wastewater systems has recently drawn widespread attention, and then developing a novel and green extracting technology has also become an enormous challenge. Herein, a facile hydrothermal method was employed to fabricate cobalt-incorporated cryptomelane-type manganese oxide molecular sieve (Co-OMS-2) for extraction Eu(III) from wastewater under diverse experimental conditions. All kinds of characterized techniques, such as SEM, TEM, XRD, FTIR, BET, EDS and XPS had verified the qualified synthesis process and splendid structural features of the Co-OMS-2. The maximum adsorption capacity of Co-OMS-2 was 7.62 × 10^-4 mol/g for Eu(III) at 298 K, which was superior than primarily traditional materials reported previous literatures. The high adsorption capacity of Eu(III) onto Co-OMS-2 was primarily attributed to high specific surface area and abundant surface functional groups, and the interactions were mainly contributed to strong surface complexation and electrostatic attraction. Under the condition of low pH, the outer-sphere surface complexation and cation exchange were primary mechanisms to Eu(III) adsorption onto Co-OMS-2 composites, while inner-sphere surface complexation was mainly assigned to Eu(III) adsorption onto Co-OMS-2 under the high pH sections. The Co-OMS-2 composite achieved equilibrium in a relatively short time, and this excellent performance was conducive to the treatment of Eu(III) under the extreme emergency conditions. In view of the extraordinary adsorption capacity and recycled reusability, the Co-OMS-2 composites can be as prospective adsorbents adopted for the extraction of Eu(III) in real wastewater management.

Noble metal nanoparticles (Mx = Ag, Au, Pd) decorated graphitic carbon nitride nanosheets for ultrafast catalytic reduction of anthropogenic pollutant, 4-nitrophenol

We report an effective facile immobilization of noble nanoparticles (M_x = Ag, Au and Pd) assembled on g-C₃N₄ (g-CN) prepared via a simple ultra-sonication strategy. The M_x assembled g-CN nanocomposites were applied for the effective conversion of 4-nitrophenol (4-NP). As prepared nanocomposites were characterized by techniques of XRD, SEM-EDS, TEM, XPS, and FT-IR analysis to gain crystallographic structural, and morphological insights. The Pd@g-C₃N₄ (Pd@g-CN) nanocomposite exhibited best catalytic performance (k_app = 1.141 min^-1) toward the conversion of 4-NP to 4-aminophenol (4-AP), almost 100% within 4 min using aqueous sodium borohydride (NaBH₄). The higher catalytic efficiency of Pd@g-CN could be attributed to the surface electron density on the Pd and rapid electron transfer capacity. Interestingly, g-CN not only role as a stabilizer but also provided compatibility for noble metal deposition, which improves the chemical and morphological stability of noble metal nanoparticles. Different reaction parameters including concentrations of 4-NP, and catalyst amount were studied. These unique combinations make noble metal nanoparticles anchored g-CN nanosheets an ideal platform for catalysis applications and environmental remediation.

Direct Z-Scheme AgBr/β-MnO2 Photocatalysts for Highly Efficient Photocatalytic and Anticancer Activity

The preparation of visible light-responsive efficient photocatalysts for removing organic contaminants from water and killing cancer cells has gotten a lot of attention due to the growing global concern. In this study, we have successfully fabricated an efficient AgBr/β-MnO₂ nanocomposite via a facile deposition and precipitation method at room temperature. Techniques such as XRD, SEM-EDS, TEM, DRS, PL, EIS, ESR, and FTIR were used to determine the crystalline, structural, morphological, optical, and other properties. The SEM and TEM analyses reveal that AgBr NPs are decorated on the surface of β-MnO₂, which possesses rods with a sphere-like structure for AgBr/β-MnO₂. The EDX analysis confirms the existence of Mn, O, Ag, and Br elements in the nanocomposites without an extra peak, indicating that the synthesized samples are highly pure. The high photocatalytic performance of AgBr/β-MnO₂ could be attributed to the formation of Ag NPs and the construction of the Z-scheme heterojunction between AgBr and β-MnO₂. This may enhance fast light absorption and efficient photogenerated (e-/h+) pairs, as indicated by EIS and photoluminescence measurements, which in turn achieved high activity for the decomposition of MB (97%, in 12 min), RhB (98.9%, in 9 min), and paracetamol (80%, in 180 min), respectively. The kinetic model study proposed that the first-order model showed a better fit than the zero- and second-order for the photocatalytic decolorization of RhB dye. XRD analysis of 0.2 AgBr/β-MnO₂ before and after recycling confirms the high stability of the catalyst. HPLC results showed that no detectable by-products are produced through the decomposition of paracetamol. Interestingly, 0.2 AgBr/β-MnO₂ nanocomposites showed visible light-induced anticancer activity against A549 cancer cell lines. The mechanistic degradation pathway has been proposed using the involvement of active species like superoxide radicals (^-•O₂) and photoinduced holes (h⁺). The proposed work focuses on synthesizing effective photocatalysts in a less hazardous environment with superior biological activity.

Synthesis of ternary-based visible light nano-photocatalyst for decontamination of organic dyes-loaded wastewater

The release of dyes-loaded wastewater from various industries is a major threat to human beings due to their health hazard effects. Ternary ferrites-based visible light photocatalyst Fe₂Zn_0.5Cu_0.5 O₄-CM (CZF-CM) was formed via the co-precipitation method. These prepared ternary ferrites nanoparticles Fe₂Zn_0.5Cu_0.5O₄ (CZF-NPs) and photocatalyst (CZF-CM) were analyzed using different spectroscopic techniques. The average crystallite size of CZF-NPs was calculated from XRD data using Scherer's equation and found to be 12 nm. The elemental composition of the synthesized ternary ferrites nanoparticles (CZF-NPs) was defined by the EDX images. The morphology of CZF-CM photocatalyst is spherical, having a smooth surface and average microspheres size of 810 μm based on SEM micrographs. The photocatalyst has bandgap of 2.57 eV, which lies in the visible range of the electromagnetic spectrum derived by extrapolating Tauc's plot. Photocatalyst CZF-CM showed 94% degradation efficiency for Rhodamine B (RB) dye at optimized conditions of initial dye concentration, catalyst dosage, pH and sunlight irradiation contact time as 40 ppm, 0.7 g, pH 8 and 125 min, respectively. Maximum degradation (96%) of methyl orange (MO) dye occurred at pH 6, at similar optimized conditions as the RB dye. The binary ferrites photocatalyst Fe₂CuO₄-CM (CF-CM) and Fe₂ZnO₄-CM (ZF-CM) of the selected metals showed lesser photocatalytic efficiency than ternary ferrites. An artificial neural network in addition to the response surface methodology was used for the optimization process. The artificial neural network is highly in agreement with the experimental results obtained for the selected dyes. The corresponding predicted response for each data set from ANOVA showed high R², R²_adj, and R²_pred values for the proposed model. It also indicates that contributing parameters in the model are significant due to having very high F-values and low p-values. It is concluded that the synthesized photocatalysts are considered an efficient entrant for the decolorization of industrial wastewater.

Electromagnetic Interference Shielding Effectiveness of Room Temperature Fabricated Manganese Dioxide/Carbon Dots Nanocomposites

The present work is focused on the fabrication of manganese dioxide/carbon dots (MnO₂/CDs) nanocomposites at room temperature in situ co-participation method in an aqueous medium and characterized. Our study showed that the concentration of CDs controls the morphology of MnO₂/CDs nanocomposite and also acted as a reducing agent to convert potassium permanganate (KMnO₄) to MnO₂. Subsequently, nanoflowers, quasi-spherical particles, broken, and interconnected chain type of morphology was observed by adding dispersion of 0.5, 1.0, 1.5, and 2.0 ml CDs in acetone to 1 mmol KMnO₄ aqueous solution in the corresponding MnO₂/CDs-0.5, MnO₂/CDs-1.0, MnO₂/CDs-1.5, and MnO₂/CDs-2.0 composites, respectively. A plausible mechanism on the transformation of morphology of MnO₂/CDs with CDs concentration is also provided. Further, the present work also focused for the first time on the application in the electromagnetic interference (EMI) shielding of MnO₂/CD nanocomposites due to the high dielectric and conductivity. Interestingly, MnO₂/CDs-2.0 (nanochains) exhibited the highest total EMI shielding efficiency (SE_T) of ~39.4 dB following reflection as dominant shielding mechanism due to the high aspect ratio, highest conductivity, high dielectric loss, and impendence mismatch.

A review of the phytochemical mediated synthesis of AgNP (silver nanoparticle): the wonder particle of the past decade

Silver nanoparticle (AgNP) has been one of the most commonly used nanoparticles since the past decade for a wide range of applications, including environmental, agricultural, and medical fields, due to their unique physicochemical properties and ease of synthesis. Though chemical and physical methods of fabricating AgNPs have been quite popular, they posed various environmental problems. As a result, the bioinspired route of AgNP synthesis emerged as the preferred pathway for synthesis. This review focuses extensively on the biosynthesis of AgNP-mediated through different plant species worldwide in the past 10 years. The most popularly utilized application areas have been highlighted with their in-depth mechanistic approach in this review, along with the discussion on the different phytochemicals playing an important role in the bio-reduction of silver ions. In addition to this, the environmental factors which govern their synthesis and stability have been reviewed. The paper systematically analyses the trend of research on AgNP biosynthesis throughout the world through bibliometric analysis. Apart from this, the feasibility analysis of the plant-mediated synthesis of nanoparticles and their applications have been intrigued considering the perspectives of engineering, economic, and environmental limitations. Thus, the review is not only a comprehensive summary of the achievements and current status of plant-mediated biosynthesis but also provides insight into emerging future research frontier.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13204-021-02135-5.

Tailoring the bandgap of Mn3O4 for visible light driven photocatalysis

The photocatalytic activity of pure Mn₃O₄ and silver (Ag) modified Mn₃O₄ nanoparticles have been investigated. The nanoparticles were prepared by using co-precipitation technique. The structural analysis showed that the Ag modified Mn₃O₄ was successfully synthesized. For instance, a slight shift to lower angle of XRD pattern was observed after Ag doping. Morphological analysis revealed that the particles have an average size of 274 nm, 287 nm and 321 nm for pure, 1% and 3% Ag modified Mn₃O₄ respectively. The UV-Visible analysis indicated that the bandgap of Mn₃O₄ decreased with increased Ag content and the band gap is 1.4 eV with the 3% of Ag content. The spectra obtained from DRS were also evaluated through inverse logarithmic derivative method (ILD) to counter check the bandgap values. 3% Ag-modified photocatalysts exhibited the enhanced decolorization efficiency compared to pure Mn₃O₄ nanoparticles. The pseudo first order kinetic model is used to explain the photocatalytic kinetics of the photocatalyst. The rate constant values are 0.01/min, 0.017/min and 0.024/min for pure Mn₃O₄, 1% Ag and 3% Ag modified Mn₃O₄ nanoparticles, respectively.

Straightforward Synthesis of Mn3O4/ZnO/Eu2O3-Based Ternary Heterostructure Nano-Photocatalyst and Its Application for the Photodegradation of Methyl Orange and Methylene Blue Dyes

Zinc oxide-ternary heterostructure Mn₃O₄/ZnO/Eu₂O₃ nanocomposites were successfully prepared via waste curd as fuel by a facile one-pot combustion procedure. The fabricated heterostructures were characterized utilizing XRD, UV-Visible, FT-IR, FE-SEM, HRTEM and EDX analysis. The photocatalytic degradation efficacy of the synthesized ternary nanocomposite was evaluated utilizing model organic pollutants of methylene blue (MB) and methyl orange (MO) in water as examples of cationic dyes and anionic dyes, respectively, under natural solar irradiation. The effect of various experimental factors, viz. the effect of a light source, catalyst dosage, irradiation time, pH of dye solution and dye concentration on the photodegradation activity, was systematically studied. The ternary Mn₃O₄/ZnO/Eu₂O₃ photocatalyst exhibited excellent MB and MO degradation activity of 98% and 96%, respectively, at 150 min under natural sunlight irradiation. Experiments further conclude that the fabricated nanocomposite exhibits pH-dependent photocatalytic efficacy, and for best results, concentrations of dye and catalysts have to be maintained in a specific range. The prepared photocatalysts are exemplary and could be employed for wastewater handling and several ecological applications.

Mesoporous ferromagnetic manganese ferrite nanoparticles for enhanced visible light mineralization of azoic dye into nontoxic by-products

In this study, a one pot facile synthesis of ferromagnetic manganese ferrite nanoparticles (MnFe₂O₄) was carried out using chemical co-precipitation method for mineralization of azo dye (Congo red (CR)) in aqueous solution under visible light irradiation. The synthesized MnFe₂O₄ nanoparticles were highly crystalline and showed face-centred cubic (FCC) structure with average particle size of 58 ± 4 nm. The BET analysis of the MnFe₂O₄ nanoparticles revealed the mesoporous distribution of material with high surface area can provide large electro active sites and short diffusion paths for the transport of ions which plays a vital role in the photocatalytic degradation of CR. The point of zero charge (pH_PZC) was observed to be 6.7 indicating favourable condition for material-anionic dye interaction. The XPS studies revealed that the large amounts of oxygen vacancies were produced due to the defects in the lattice oxygen. The MnFe₂O₄ nanoparticles mineralised 98.3 ± 0.2% of 50 mg/L CR within 30 min when tested in photocatalytic reactor under 565 nm. The particles were recoverable under the influence of an external magnet after the photocatalytic reaction and were reusable. The recovered nanoparticles showed 96% of CR degradation efficiency even after five cycles of reuse. The by-product analysis with GC-MS indicated mineralization of CR into simple alcohols and acids. The aqueous solution containing mineralised CR was nontoxic to Trigonella foenumgraecum and Vigna mungo seeds and favoured increased germination, plumule and radicle length when compared to untreated CR.

Phytomediated Photo-Induced Green Synthesis of Silver Nanoparticles Using Matricaria chamomilla L. and Its Catalytic Activity against Rhodamine B

The bio-fabrication of silver nanoparticles (AgNPs) was carried out through the facile green route, using the aqueous extract of Matricaria chamomilla L. Herein, we have developed a cost-efficient, ecofriendly, and photo-induced method for the biomolecule-assisted synthesis of AgNPs using an aqueous extract of Matricaria chamomilla L. as a bio-reducing and capping/stabilizing agent. The biomolecule-capped AgNPs were confirmed from the surface plasmon resonance (SPR) band at λmax = 450 nm using a UV-visible spectrometer. The stability of the AgNPs was confirmed by recording the UV-visible spectra for a more extended period, and no precipitation was observed in the sol. The morphology and structure of photo-induced biomolecule-capped AgNPs were characterized by different microscopic and spectroscopy techniques such as TEM, SEM, EDX, XRD, and FTIR analysis. The role of phytochemicals as reducing and stabilizing agents was confirmed by comparative FTIR analysis of the AgNPs and pure Matricaria chamomilla L. aqueous extract. The obtained result shows that the AgNPs are mostly spherical morphology with an average size of about 26 nm. Furthermore, the thermal stability of biomolecule-capped AgNPs was examined by TGA-DTG analysis that showed a weight loss of approximately 36.63% up to 800 °C. Moreover, the potential photocatalytic activity of photo-induced AgNPs against Rhodamine B (RB) was examined in the presence of UV light irradiation. The catalyst reusability, the effect of catalyst dosage and initial dye concentration, and the effect of the temperature and pH of the reaction medium were also assessed.

Multi-functional MnO2 nanomaterials for photo-activated applications by a plasma-assisted fabrication route

Supported MnO2-based nanomaterials were fabricated on fluorine-doped tin oxide substrates using plasma enhanced-chemical vapor deposition (PE-CVD) between 100 °C and 400 °C, starting from a fluorinated Mn(ii) diamine diketonate precursor. Growth experiments yielded β-MnO2 with a hierarchical morphology tuneable from dendritic structures to quasi-1D nanosystems as a function of growth temperature, whose variation also enabled a concomitant tailoring of the system fluorine content, and of the optical absorption and band gap. Preliminary photocatalytic tests were aimed at the investigation of photoinduced hydrophilic (PH) and solid phase photocatalytic (PC) performances of the present nanomaterials, as well as at the photodegradation of Plasmocorinth B azo-dye aqueous solutions. The obtained findings highlighted an attractive system photoactivity even under visible light, finely tailored by fluorine content, morphological organization and optical properties of the prepared nanostructures. The results indicate that the synthesized MnO2 nanosystems have potential applications as advanced smart materials for anti-fogging/self-cleaning end uses and water purification.

The design of novel visible light driven Ag/CdO as smart nanocomposite for photodegradation of different dye contaminants

In this paper, we report a novel visible light driven Ag/CdO photocatalyst, fabricated for the first time via one pot hydrothermal method and further applied for the photodegradation of two important exemplar water contaminants, Malachite green and Acid Orange 7. The microstructure, composition and optical properties of Ag/CdO nanocomposites were thoroughly investigated by various techniques. Scanning electron microscopy clearly shows that Ag NPs were strongly embedded between the CdO nanoparticles. Among the series of synthesized Ag/CdO nanocomposites, (5%) Ag/CdO nanocomposite possesses enhanced photocatalytic activity. This result was attributed to the synergistic effect between Ag and CdO, and mainly Ag NPs can act as an electron trap site, which could reduce the recombination of the electron-hole and induce the visible light absorption. The active species trapping experiments implicate OH and O₂^- radicals as the respective primary and secondary reactive species responsible for oxidative photodegradation of organic pollutants. On the basis of the results, a possible photocatalytic mechanism has also been proposed.

Removal of PFOA in groundwater by Fe0 and MnO2 nanoparticles under visible light

The main objective of this study was to find a cost-effective, efficient and environmentally-friendly solution to remove perfluorooctanic acid (PFOA) from groundwater by using Fe⁰ and MnO₂ nanoparticles. The selected method was expected to be applicable to the remediation of PFOA-contaminated groundwater. Phytotoxicity of the nanoparticle treatment was studied to demonstrate the safe application of the nanomaterials. Zero-valent Fe (100 mg L^-1) and MnO₂ (100 mg L^-1) nanoparticles, produced in our lab, were used to remove PFOA up to 10 mg L^-1. The test was conducted under visible light with or without addition of 0.88 mol L^-1 H₂O₂ in a pH range of 0.5-11.0 for a duration of 18 h. Using Fe nanoparticles, a higher percentage of PFOA was removed under extreme acidic environment of pH 0.5 than under the basic environment of pH 11.0, and a minimum removal rate was reached under the neutral environment. The Fe nanoparticles were more efficient than the MnO₂ nanoparticles at pH 0.5 with a removal rate of 69.7% and 89.7% without and with H₂O₂ addition, respectively. Phytotoxicity study showed that the treatment by Fe nanoparticles under mild pH reduced the phytotoxicity of groundwater-associated PFOA to Arabidopsis thaliana. The Fe nanoparticles did not show negative effect to A. thaliana under the experimental conditions used in this study.

Morphology and phase tuning of α- and β-MnO2 nanocacti evolved at varying modes of acid count for their well-coordinated energy storage and visible-light-driven photocatalytic behaviour

α and β of MnO₂ nanocacti (comprising nanowires with 1–10 nm diameter self assembled by ultrathin sheets) as well as MnO₂ nanorods (10–40 nm diameter) are synthesized without any seed or template.