Biosynthesis of SnO2 Nanoparticles Using Bacterium Erwinia herbicola and Their Photocatalytic Activity for Degradation of Dyes

A Review on Nanomaterial as Photocatalysts for Degradation of Organic Pollutants

Eliminating hazardous organic contaminants from water is a major concern today. Nanomaterials with their textural features, large surface area, electrical conductivity, and magnetic properties make them efficient for the removal and photocatalytic degradation of organic pollutants. The reaction mechanisms of the photocatalytic oxidation of common organic pollutants were critically examined. A detailed review of articles published on photocatalytic degradation of hydrocarbons, pesticides, and dyes was presented therein. This review seeks to bridge information gaps on the reported nanomaterial as photocatalysts for the degradation of organic pollutants under sub-headings, nanomaterials, organic pollutants, degradation of organic pollutants, and mechanisms of photocatalytic activities.

Natural waste-derived nano photocatalysts for azo dye degradation

Due to their widespread application in water purification, there is a significant interest in synthesising nanoscale photocatalysts. Nanophotocatalysts are primarily manufactured through chemical methods, which can lead to side effects like pollution, high-energy usage, and even health issues. To address these issues, "green synthesis" was developed, which involves using plant extracts as reductants or capping agents rather than industrial chemical agents. Green fabrication has the benefits of costs less, pollution reduction, environmental protection and human health safety, compared to the traditional methods. This article summarises recent advances in the environmentally friendly synthesis of various nanophotocatalysts employed in the degradation of azo dyes. This study compiles critical findings on natural and artificial methods to achieve the goal. Green synthesis is constrained by the time and place of production and issues with low purity and poor yield, reflecting the complexity of plants' geographical and seasonal distributions and their compositions. However, green photocatalyst synthesis provides additional growth opportunities and potential uses.

Hydrothermal synthesis of V2O5/TiO2 decorated graphitic carbon nitride nanocomposite for biomolecule oxidation inhibition and dye degradation applications

Oxides of vanadium, titanium and graphitic carbon nitride (g-C3N4) are well known for their catalytic activities. In order to achieve synergic catalytic effects, a novel nanocomposite (NC) i.e. V2O5/TiO2/g-C3N4 has been synthesized by a very simple, ecofriendly and nonhazardous hydrothermal method. The fabricated NC was characterized employing UV-Visible, FTIR, SEM, and XRD techniques. UV-Visible and FTIR analysis indicated the formation of the nanocomposite and XRD analysis confirmed the association of V2O5 and TiO2 with g-C3N4 in nanocomposite. SEM study indicated the hetero-structure of NC having size ranging from 50 to 80 nm and it was found having hexagonal crystallite structure. The synthesized nanocomposite exhibited excellent scavenging of free radicals DPPH● (91%) and ABTS●+ (64%) that are responsible for the oxidation of biomolecules. Therefore, NC can be claimed having biomolecule oxidation protective potential. In addition, photocatalytic ability for the degradation of methylene blue (MB) and methyl orange (MO) was also achieved up to 94% and 89% respectively. The synthesized novel nanocomposite exhibited excellent potential to remove free radicals and dyes from aqueous medium which can be further used for the environmental remediation.

Biogenic Selenium Nanoparticles in Biomedical Sciences: Properties, Current Trends, Novel Opportunities and Emerging Challenges in Theranostic Nanomedicine

Selenium is an important dietary supplement and an essential trace element incorporated into selenoproteins with growth-modulating properties and cytotoxic mechanisms of action. However, different compounds of selenium usually possess a narrow nutritional or therapeutic window with a low degree of absorption and delicate safety margins, depending on the dose and the chemical form in which they are provided to the organism. Hence, selenium nanoparticles (SeNPs) are emerging as a novel therapeutic and diagnostic platform with decreased toxicity and the capacity to enhance the biological properties of Se-based compounds. Consistent with the exciting possibilities offered by nanotechnology in the diagnosis, treatment, and prevention of diseases, SeNPs are useful tools in current biomedical research with exceptional benefits as potential therapeutics, with enhanced bioavailability, improved targeting, and effectiveness against oxidative stress and inflammation-mediated disorders. In view of the need for developing eco-friendly, inexpensive, simple, and high-throughput biomedical agents that can also ally with theranostic purposes and exhibit negligible side effects, biogenic SeNPs are receiving special attention. The present manuscript aims to be a reference in its kind by providing the readership with a thorough and comprehensive review that emphasizes the current, yet expanding, possibilities offered by biogenic SeNPs in the biomedical field and the promise they hold among selenium-derived products to, eventually, elicit future developments. First, the present review recalls the physiological importance of selenium as an oligo-element and introduces the unique biological, physicochemical, optoelectronic, and catalytic properties of Se nanomaterials. Then, it addresses the significance of nanosizing on pharmacological activity (pharmacokinetics and pharmacodynamics) and cellular interactions of SeNPs. Importantly, it discusses in detail the role of biosynthesized SeNPs as innovative theranostic agents for personalized nanomedicine-based therapies. Finally, this review explores the role of biogenic SeNPs in the ongoing context of the SARS-CoV-2 pandemic and presents key prospects in translational nanomedicine.

A critical review on application of organic, inorganic and hybrid nanophotocatalytic assemblies for photocatalysis of methyl orange dye in aqueous medium

Methyl orange (MO) is a highly carcinogenic and harmful contaminant, which has been extensively reported for its detrimental impact on human and aquatic life. The photodegradation of MO into less toxic products has gained much attention over the past few decades. Herein we have reviewed the recent advancement in designing of nanomaterials (NMs) stabilized on different fabricating assemblies and their application in photocatalysis of MO dye. These photocatalytic systems possess various advantages and disadvantages. Graphene-based supported materials on different NMs are highly reported photocatalysts for photocatalysis of MO dye. Recent advancement, parameters affecting photocatalytic studies, kinetics and photocatalytic mechanism of MO have been thoroughly explained in this review. Future outcomes are also provided for extending the development of scientific research in this field.

SnO2 Nanoparticles: Green Synthesis, Characterization, and Water Treatment

The green synthesis approach was utilized to synthesize tin dioxide (SnO2) nanoparticles (NPs) using Ocimum Basilicum leaves extract with different concentrations (10, 15, 20 ml) and different reaction temperatures (30, 60, 90 °C). The green synthesis method is considered economical, environmentally friendly, and non-toxic. X-ray diffraction patterns of the synthesized SnO2 NPs have displayed a tetragonal crystalline structure. The crystallite size of SnO2 NPs increased from 15.12 to 17.9 nm with increasing reaction temperature while decreasing from 20.68 to 17.9 nm with increasing extract concentrations. The morphology of the synthesized SnO2 NPs was investigated using high-energy transmission electron microscopy (HR-TEM). The optical energy gap was determined using the diffuse reflectance UV–vis spectra range (300–1200) nm of SnO2 NPs at different reaction temperatures and different extract concentrations. UV/Visible Spectrophotometer was used for studying the photodegradation of methylene blue dye (MB) dye. The photocatalytic degradation of MB revealed that SnO2 NPs at reaction temperature 90 °C degraded 69% of MB solution when exposed to UV illumination for 90 min while the degradation reaches 90% for 180 min of exposure. It was obvious that the degradation rate of MB was increased with the increase of reaction temperature, and the extract concentration.

In-vitro toxicity assessment of a textile dye Eriochrome Black T and its nano-photocatalytic degradation through an innovative approach using Mf-NGr-CNTs-SnO2 heterostructures

The present study aimed to assess the in-vitro toxicity of a popular azodye, Eriochrome Black T (EBT) which may be an environmental hazard causing water pollution if released by textile industries as waste effluents to nearby water ponds. We explored the toxic potential of EBT at 200, 400 and 800 μg/ml concentrations, which were selected based on quantification of EBT present in the pond water near carpet industries. We investigated the permeability of EBT across the organ barriers and found it to be 6.48 ± 0.44% at the highest concentration. EBT also showed up to 26.46 ± 0.533% hemolytic potential on human RBCs. MTT assay revealed toxicity of up to 64.9 ± 10.12%. A dose-dependent increase in intracellular ROS levels and Caspase 3/7 activity was observed and confocal microscopy also demonstrated a similar trend of cellular apoptosis indicating ROS mediated induction of apoptosis as a mechanism of EBT induced cytotoxicity. After establishing the toxicity of EBT, an innovative nano-photocatalytic approach for dye remediation was applied by using as synthesized Mf-NGr-CNTs-SnO₂ heterostructures. This catalyst showed dye degradation potential of up to 82% in 2 h in the presence of sun light. The degraded dye products were tested to have up to 30% reduced cellular toxicity as compared to the parent compound. This work successfully establishes the toxicity of EBT along with devising an innovative approach towards dye degradation where the catalyst is adhered on melamine foam and not being mixed in the effluents directly, thereby, reducing the possibility of catalyst being leached out into the river water.

Construction of SnO2/g-C3N4 an effective nanocomposite for photocatalytic degradation of amoxicillin and pharmaceutical effluent

The current study mainly focused on the fabrication of 2D graphitic carbon nitride-supported tin oxide nanoparticles (SnO₂/g-C₃N₄) for the effective degradation of Amoxicillin (AMX). Tin oxide (SnO₂) NPs were prepared by green and easy modification technique, and then it is decorated over g-C₃N₄ nanosheets. The structural morphology and surface composition of the synthesized SnO₂/g-C₃N₄ nanocomposite were fully analysed by UV-Vis, XRD, XPS, and HR-SEM with EDAX, FT-IR, and BET analysis. The (HR-TEM) microscopy, the size of SnO₂ NPs which as a diameter is about 6.2 nm. The Raman analysis revealed that the SnO₂/g-C₃N₄ composite had a moderate graphitic structure, with a measured I_D/I_g value of 0.79. The degradation efficiency of antibiotic pollutant AMX and pharma effluent treatment was monitored by UV spectroscopy. The optical band gap of SnO₂ (2.9 eV) and g-C₃N₄ (2.8 eV) photocatalyst was measured by Tauc plots. To investigate the mechanism through the photodegradation efficiency of the catalyst was analysed by using different Scavenger EDTA-2Na holes (h⁺) has a greater contribution towards the degradation process. Under visible irradiation, SnO₂/g-C₃N₄ nanocomposite has exhibited an excellent degradation performance of 92.1% against AMX and 90.8% for pharmaceutical effluent in 80 min.

A study of the structural, morphological, and optical properties of shock treated SnO2 nanoparticles: removal of Victoria blue dye

In this work, Tin Oxide (SnO₂) nanoparticles (NPs) were prepared by green microwave followed by hydrothermal methods, using tea extract as a reducing agent. To verify the stability of physical and chemical properties of SnO₂ NPs, samples were subjected to shock impulsion experimentation. Different characterization techniques were employed to analyze the crystallinity, molecular structure, and optical parameters of the control SnO₂ and shock wave exposed SnO₂ NPs. Powder X-ray diffraction (PXRD) revealed no significant change in crystal structure. Williamson – Hall analysis demonstrates that the stress and strain between Sn–O changes during the impulsion of shocks. Rietveld analysis reveals change in the bond length between Sn–O. The molecular structure is not affected during shock loading, but the optical properties do change. From the photocatalytic experiment, we find that the parameters such as stress, strain, and bond length make an enormous impact in photocatalytic application.

Green Biosynthesis of Tin Oxide Nanomaterials Mediated by Agro-Waste Cotton Boll Peel Extracts for the Remediation of Environmental Pollutant Dyes

The sustainable synthesis of metal oxide materials provides an ecofriendly and more exciting approach in the domain of a clean environment. Besides, plant extracts to synthesize nanoparticles have been considered one of the more superior ecofriendly methods. This paper describes the biosynthetic preparation route of three different sizes of tetragonal structure SnO₂ nanoparticles (SNPs) from the agro-waste cotton boll peel aqueous extract at 200, 500, and 800 °C for 3 h and represents a low-cost and alternative preparation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectrophotometry, ultraviolet-visible absorption spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy. Surface area and porosity size distribution were identified by nitrogen adsorption-desorption isotherms and Brunauer-Emmett-Teller analysis. The photocatalytic properties of the SNP samples were studied against methylene blue (MB) and methyl orange (MO), and the degradation was evaluated with three different size nanomaterials of 3.97, 8.48, and 13.43 nm. Photocatalytic activities were carried out under a multilamp (125 W Hg lamps) photoreactor. The smallest size sample exhibited the highest MB degradation efficiency within 30 min than the most significant size sample, which lasted 80 min. Similarly, in the case of MO, the smallest sample showed a more superior degradation efficiency with a shorter period (40 min) than the large-size samples (100 min). Therefore, our studies suggested that the developed SNP nanomaterials could be potential, promising photocatalysts against the degradation of industrial effluents.

Biosynthesis, characterization, and evaluation of antibacterial and photocatalytic methylene blue dye degradation activities of silver nanoparticles from Streptomyces tuirus strain

Silver nanoparticles (AgNPs) are a promising technology for the design of antimicrobial agents against drug-resistant pathogens. It could also be used for the photocatalytic degradation of dyes used in industries such as methylene blue (MB). In this study, 17 different actinomycetal strains isolated from hydrocarbon-contaminated soils collected from an oil distribution company in Algeria were evaluated for their ability to produce NPs. After a selection process, S16 was the main strain capable of synthesizing AgNPs extracellularly. The strain S16 was determined using molecular identification based on the sequencing of the 16S rDNA gene. Among various techniques used for the synthesis of AgNPS, a technique using a temperature of 30 °C, pH of 7, a metal salt concentration of 1 mM, and a period of 72 h in the dark were found to be more effective in the biosynthesis of the AgNPs. The biosynthesized AgNPs that were analyzed by UV-visible spectroscopy resulted in a specific peak at a wavelength of (λ = 400 nm). The DRX analyses showed characteristic peaks of the AgNPs at (1 1 1), (2 0 0), (2 2 2), and (3 1 1), which validated the presence and crystalline nature of the biosynthesized NPs. Zetasizer analysis showed an average size and zeta potential of 64 nm (-32.3 mV), while the SEM-EDS analysis confirmed the spherical shape of AgNPs and the presence of Ag atoms in the elemental composition. The biosynthesized AgNPs indicated adequate antibacterial activity against 5 out of the 6 strains tested in this study, using minimum inhibitory concentration (MIC) that ranged from 217.18 μg/mL to 1137.5 μg/mL. The AgNPs were combined with commercial antibiotics and the synergistic effect of the combination was also assessed against MRSA which resulted in increased antibacterial activity of AgNPs in the presence of the strain S16. Furthermore, the photocatalytic degradation of the methylene blue (MB) was evaluated under sunlight and UV irradiations using biosynthesized AgNPs. The AgNPs showed photocatalytic decolorization potential of 71.3% for MB dye (20 ppm) under sunlight irradiation within 6 h of incubation, while only 11.25% of the MB dye degraded using UV irradiation.

Tin oxide based nanostructured materials: synthesis and potential applications

In view of their inimitable characteristics and properties, SnO₂ nanomaterials and nanocomposites have been used not only in the field of diverse advanced catalytic technologies and sensors but also in the field of energy storage such as lithium-ion batteries and supercapacitors, and in the field of energy production such as solar cells and water splitting. This review discusses the various synthesis techniques such as traditional methods, including processes like thermal decomposition, chemical vapor deposition, electrospinning, sol-gel, hydrothermal, solvothermal, and template-mediated methods and green methods, which include synthesis through plant-mediated, microbe-mediated, and biomolecule-mediated processes. Moreover, the advantages and limitations of these synthesis procedures and how to overcome them that would lead to future research are also discussed. This literature also focuses on various applications such as environmental remediation, energy production, energy storage, and removal of biological contaminants. Therefore, the rise and journey of SnO₂-based nanocomposites will motivate the modern generation of chemists to modify and design robust nanoparticles and nanocomposites that can effectively tackle significant environmental challenges. This overview concludes by providing future perspectives on research into tin oxide in synthesis and its various applications.

Biological Synthesis of Nanocatalysts and Their Applications

Over the past few decades, the synthesis and potential applications of nanocatalysts have received great attention from the scientific community. Many well-established methods are extensively utilized for the synthesis of nanocatalysts. However, most conventional physical and chemical methods have some drawbacks, such as the toxicity of precursor materials, the requirement of high-temperature environments, and the high cost of synthesis, which ultimately hinder their fruitful applications in various fields. Bioinspired synthesis is eco-friendly, cost-effective, and requires a low energy/temperature ambient. Various microorganisms such as bacteria, fungi, and algae are used as nano-factories and can provide a novel method for the synthesis of different types of nanocatalysts. The synthesized nanocatalysts can be further utilized in various applications such as the removal of heavy metals, treatment of industrial effluents, fabrication of materials with unique properties, biomedical, and biosensors. This review focuses on the biogenic synthesis of nanocatalysts from various green sources that have been adopted in the past two decades, and their potential applications in different areas. This review is expected to provide a valuable guideline for the biogenic synthesis of nanocatalysts and their concomitant applications in various fields.

Exploration of Microbial Factories for Synthesis of Nanoparticles - A Sustainable Approach for Bioremediation of Environmental Contaminants

The nanomaterials synthesis is an intensifying research field due to their wide applications. The high surface-to-volume ratio of nanoparticles and quick interaction capacity with different particles make them as an attractive tool in different areas. Conventional physical and chemical procedures for development of metal nanoparticles become outmoded due to extensive production method, energy expenditure and generation of toxic by-products which causes significant risks to the human health and environment. Hence, there is a growing requirement to search substitute, non-expensive, reliable, biocompatible and environmental friendly methods for development of nanoparticles. The nanoparticles synthesis by microorganisms has gained significant interest due to their potential to synthesize nanoparticles in various sizes, shape and composition with different physico-chemical properties. Microbes can be widely applied for nanoparticles production due to easy handling and processing, requirement of low-cost medium such as agro-wastes, simple scaling up, economic viability with the ability of adsorbing and reducing metal ions into nanoparticles through metabolic processes. Biogenic synthesis of nanoparticles offers clean, non-toxic, environmentally benign and sustainable approach in which renewable materials can be used for metal reduction and nanoparticle stabilization. Nanomaterials synthesized through microbes can be used as a pollution abatement tool as they also contain multiple functional groups that can easily target pollutants for efficient bioremediation and promotes environmental cleanup. The objective of the present review is to highlight the significance of micro-organisms like bacteria, actinomycetes, filamentous fungi, yeast, algae and viruses for nanoparticles synthesis and advantages of microbial approaches for elimination of heavy metals, dyes and wastewater treatment.

Disinfection mechanism of the photocatalytic activity of SnO2 thin films against Candida albicans, proposed from experimental and simulated perspectives

Nosocomial infections are an important health problem and cause of complications and death in hospitalized patients. This problem should be solved from the preventive angle, avoiding the spread of infections by designing disinfection methods based on the photocatalytic activity of semiconductor materials such as tin oxide (SnO₂). The antimicrobial activity of UV light was tested by using inoculation with Candida albicans ATCC10231 on SnO₂ thin films and counting colony forming units (CFU). The interaction of UV light with SnO₂ was analyzed by density functional theory (DFT) and the extension to the Hubbard model (DFT+U) schemes to predict the electron behavior at the subatomic level. After exposure to UV light, C. albicans showed a reduction of 36.5% in viable cells, and when SnO₂ was included, cell viability was reduced by 60.2%. Measurements of the electronic structure obtained by the first-principle calculations under the DFT and DFT+U schemes showed that the O-p orbitals mediate the oxidation process in the bulk semiconductor. By including the surface effects when cleaving the (1 0 0) plane, the three orbitals O-p, Sn-p, and Sn-s are the mediators. SnO₂ films are promising antimicrobial coatings because UV light has a synergic activity with thin films, resulting in faster disinfection.

Green and Cost-Effective Synthesis of Tin Oxide Nanoparticles: A Review on the Synthesis Methodologies, Mechanism of Formation, and Their Potential Applications

Nanotechnology has become the most promising area of research with its momentous application in all fields of science. In recent years, tin oxide has received tremendous attention due to its fascinating properties, which have been improved with the synthesis of this material in the nanometer range. Numerous physical and chemical methods are being used these days to produce tin oxide nanoparticles. However, these methods are expensive, require high energy, and also utilize various toxic chemicals during the synthesis. The increased concerns related to human health and environmental impact have led to the development of a cost-effective and environmentally benign process for its production. Recently, tin oxide nanoparticles have been successfully synthesized by green methods using different biological entities such as plant extract, bacteria, and natural biomolecules. However, industrial-scale production using green synthesis approaches remains a challenge due to the complexity of the biological substrates that poses a difficulty to the elucidations of the reactions and mechanism of formations that occur during the synthesis. Hence, the present review summarizes the different sources of biological entities and methodologies used for the green synthesis of tin oxide nanoparticles and the impact on their properties. This work also describes the advances in the understanding of the mechanism of formation reported in the literature and the different analytical techniques used for characterizing these nanoparticles.

Microbiologically-Synthesized Nanoparticles and Their Role in Silencing the Biofilm Signaling Cascade

The emergence of bacterial resistance to antibiotics has led to the search for alternate antimicrobial treatment strategies. Engineered nanoparticles (NPs) for efficient penetration into a living system have become more common in the world of health and hygiene. The use of microbial enzymes/proteins as a potential reducing agent for synthesizing NPs has increased rapidly in comparison to physical and chemical methods. It is a fast, environmentally safe, and cost-effective approach. Among the biogenic sources, fungi and bacteria are preferred not only for their ability to produce a higher titer of reductase enzyme to convert the ionic forms into their nano forms, but also for their convenience in cultivating and regulating the size and morphology of the synthesized NPs, which can effectively reduce the cost for large-scale manufacturing. Effective penetration through exopolysaccharides of a biofilm matrix enables the NPs to inhibit the bacterial growth. Biofilm is the consortia of sessile groups of microbial cells that are able to adhere to biotic and abiotic surfaces with the help extracellular polymeric substances and glycocalyx. These biofilms cause various chronic diseases and lead to biofouling on medical devices and implants. The NPs penetrate the biofilm and affect the quorum-sensing gene cascades and thereby hamper the cell-to-cell communication mechanism, which inhibits biofilm synthesis. This review focuses on the microbial nano-techniques that were used to produce various metallic and non-metallic nanoparticles and their "signal jamming effects" to inhibit biofilm formation. Detailed analysis and discussion is given to their interactions with various types of signal molecules and the genes responsible for the development of biofilm.

Green-synthesized nanocatalysts and nanomaterials for water treatment: Current challenges and future perspectives

Numerous hazardous environmental pollutants in water bodies, both organic and inorganic, have become a critical global issue. As greener and bio-synthesized versions of nanoparticles exhibit significant promise for wastewater treatment, this review discusses trends and future prospects exploiting the sustainable applications of green-synthesized nanocatalysts and nanomaterials for the removal of contaminants and metal ions from aqueous solutions. Recent trends and challenges about these nanocatalysts and nanomaterials and their potential applications in wastewater treatment and water purification are highlighted including toxicity and biosafety issues. This review delineates the pros and cons and critical issues pertaining to the deployment of these nanomaterials endowed with their superior surface area, mechanical properties, significant chemical reactivity, and cost-effectiveness with low energy consumption, for removal of hazardous materials and contaminants from water; comprehensive coverage of these materials for industrial wastewater remediation, and their recovery is underscored by recent advancements in nanofabrication, encompassing intelligent and smart nanomaterials.

Sustainability consolidation via employment of biomimetic ecomaterials with an accentuated photo-catalytic potential: emerging progressions

Environmental pollution produced due to direct and untreated release of toxic organic pollutants such as dyes from the textile industries is not only effect the human life but also contaminates the ecosystem through different transferal modes. Green nanomaterials synthesized by using biological reducing agents offer sustainable, economically viable, facile, rapid and eco-friendly approach with photocatalytic degradation efficiencies >90% for organic dyes over the other traditional technologies. Current review has for the first time comprehensively abridged the suitability of green nanoparticles over chemogenic nanoparticles, the remediative role of these biogenic nanoparticles with major emphasis on the recent progressions in the photocatalysis of different toxic dyes and pollutants. Unlike physicochemically processed nanoparticles, biogenic nanoparticles has profound contribution to the sustainable development goals due to their cleaner and economical synthesis in addition to their detoxifying role. Meticulous review of the publications are strongly suggestive of the adoptability of biogenic nanoparticles at an implementation scale for their auspicious remediative role in addition to facile fabrication, natural reducing agents based synthetic mode, toxicity free and sustainable nature. However, the studies are also indicative of the need for utilization of biogenic synthesis at practical scale to derive maximum sustainability and ecological benefits.

Biosynthesis of inorganic nanomaterials using microbial cells and bacteriophages

Inorganic nanomaterials are widely used in chemical, electronics, photonics, energy and medical industries. Preparing a nanomaterial (NM) typically requires physical and/or chemical methods that involve harsh and environmentally hazardous conditions. Recently, wild-type and genetically engineered microorganisms have been harnessed for the biosynthesis of inorganic NMs under mild and environmentally friendly conditions. Microorganisms such as microalgae, fungi and bacteria, as well as bacteriophages, can be used as biofactories to produce single-element and multi-element inorganic NMs. This Review describes the emerging area of inorganic NM biosynthesis, emphasizing the mechanisms of inorganic-ion reduction and detoxification, while also highlighting the proteins and peptides involved. We show how analysing a Pourbaix diagram can help us devise strategies for the predictive biosynthesis of NMs with high producibility and crystallinity and also describe how to control the size and morphology of the product. Here, we survey biosynthetic inorganic NMs of 55 elements and their applications in catalysis, energy harvesting and storage, electronics, antimicrobials and biomedical therapy. Furthermore, a step-by-step flow chart is presented to aid the design and biosynthesis of inorganic NMs employing microbial cells. Future research in this area will add to the diversity of available inorganic NMs but should also address scalability and purity.

Cost-effective synthesis method of facile environment friendly SnO2 nanoparticle for efficient photocatalytic degradation of water contaminating compound

The present study demonstrates an intensive experimental work based on the tin oxide (SnO₂) nanoparticle synthesis which was successfully carried out by a simple conventional precipitation method followed by calcination at 700 °C. The synthesized nanoparticles were characterized by X-ray powder diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDAX). The XRD pattern proves that tetragonal rutile structure SnO₂ nanoparticles were formed. The crystallite particle size calculation from Scherer's equation revealed the average size of 28.5 nm. The absorption spectrum of SnO₂ nanoparticles showed absorption band at about 290 nm and the band gap energy (E_g) from Tauc plot was obtained at 3.8 eV. The photocatalytic degradation of pharmaceutical compound, 4-aminopyridine (5 ppm) using synthesized SnO₂ nanoparticle, was assessed. The effect of variable catalyst dosage, pH and irradiation sources, were studied. The optimum catalyst dosage and pH were found to be 1.5 gm/L and 6.5, respectively. The degradation efficiency of water contaminant 4-aminopyridine under UV light and solar light irradiation for 120 min were found to be 97% and 11%, respectively. The reusability of the catalyst was checked and has been found stable after three photocatalytic runs.

TiO2 decorated functionalized halloysite nanotubes (TiO2@HNTs) and photocatalytic PVC membranes synthesis, characterization and its application in water treatment

In this study photocatalyst, TiO₂@HNTs were prepared by  synthesizing TiO₂ nanoparticles in situ on the  functionalized halloysite nanotubes (HNTs) surface. Photocatalytic PVC membrane TiO₂@HNTs M2 (2 wt.%) and TiO₂@HNTs M3 (3 wt.%) were also prepared. Photocatalyst TiO₂@HNTs and photocatalytic PVC membranes were used to study the photocatalytic activity against the methylene blue (MB) and rhodamine B (RB) dyes in UV batch reactor. The structure and morphology of photocatalyst and photocatalytic PVC membrane were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), UV-Vis spectrophotometer and photoluminescence (PL). The PL study showed that the oxygen vacancies and surface hydroxyl groups present on the surface of TiO₂@HNTs act as excellent traps for charge carrier, reducing the electron-hole recombination rate.TiO₂@HNTs 2 (2 wt.%) and TiO₂@HNTs 3 (3 wt.%) degraded MB dye up to 83.21%, 87.47% and RB dye up to 96.84% and 96.87%, respectively. TiO₂@HNT photocatalyst proved to be stable during the three consecutive cycle of photocatalytic degradation of the RB dye. TiO₂@HNTs M2 and TiO₂@HNTs M3 degraded MB dye up to 27.19%, 42.37% and RB dye up to 30.78%, 32.76%, respectively. Photocatalytic degradation of both the dyes followed the first-order kinetic model. Degradation product analysis was done using the liquid chromatography–mass spectrometry (LC-MS) and the results showed that the dye degradation was initiated by demethylation of the molecule. MB and RB dye degradation reaction were tested by TBA and IPA as OH^* and H⁺ scavengers respectively. Mechanism of photocatalytic activity of TiO₂@HNTs and photocatalytic PVC membrane were also explained.

Synthesis and applications of biogenic nanomaterials in drinking and wastewater treatment

The continuous increase in water pollution by various organic & inorganic contaminants has become a major issue of concern worldwide. Furthermore, the anthropogenic activities for the manufacturing of various products have boosted this problem manifold. To overcome this serious issue, nanotechnology has initiated to explore various proficient strategies to treat waste water in a more precise and accurate way with the support of various nanomaterials. In recent times, nanosized materials have proved their applicability to provide clean and affordable water treatment technologies. The exclusive features such as high surface area and mechanical properties, greater chemical reactivity, lower cost and energy, efficient regeneration for reuse allow the nanomaterials perfect for water remediation. But the conventional routes of synthesis of nanomaterials encompass the involvement of hazardous and volatile chemicals; therefore the use of nanomaterials further creates the secondary pollution. This issue has intrigued the scientists to develop biogenic pathways and procedures which are environmentally safer and inexpensive. It has led to the new trends that involve developing bio-inspired nano-scale adsorbents and catalysts for the removal and degradation of a wide range of water pollutants. Carbohydrates, proteins, polymers, flavonoids, alkaloids and several antioxidants obtained from plants, bacteria, fungi, and algae have proven their effectiveness as capping and stabilizing agents during manufacture of nanomaterials. Application of biogenic nanomaterials for waste water treatment is relatively newer but rapidly escalating area of research. In the present review, promises and challenges for the synthesis of various biogenic nanomaterials and their potential applications in waste water treatment and/or water purification have been discussed.

Microorganism Assisted Synthesized Nanoparticles for Catalytic Applications

Metal and metalloid nanoparticles (NPs) have attracted substantial attention from research communities over the past few decades. Traditional methodologies for NP fabrication have also been intensely explored. However, drawbacks such as the use of toxic agents and the high energy consumption involved in chemical and physical processes hinder their further application in various fields. It is well known that some bacteria are capable of binding and concentrating dissolved metal and metalloid ions, thereby detoxifying their environments. Bioinspired fabrication of NPs is environmentally friendly and inexpensive and requires only low energy consumption. Some biosynthesized NPs are usually used as heterogeneous catalysts in environmental remediation and show higher catalytic efficiency because of their enhanced biocompatibility, stability and large specific surface areas. Therefore, bacteria used as nanofactories can provide a novel approach for removing metal or metalloid ions and fabricating materials with unique properties. Even though a wide range of NPs have been biosynthesized, and their synthetic mechanisms have been proposed, some of these mechanisms are not known in detail. This review focuses on the synthesis and catalytic applications of NPs obtained using bacteria. The known mechanisms of bioreduction and prospects in the design of NPs for catalytic applications are also discussed.

Biosynthesis, Characterization of Some Combined Nanoparticles, and Its Biocide Potency against a Broad Spectrum of Pathogens

The development of environmentally benign procedures for the synthesis of metallic nanoparticles (NPs) is a vital aspect in bionanotechnology applications for health care and the environment. This study describes the biosynthesis of Ag, Co, Ni, and Zn NPs by employing nanobiofactory Proteus mirabilis strain 10B. The physicochemical characterization UV-visible spectroscopy, scanning electron microscopy-energy-dispersive X-ray microanalysis (EDX), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS) technique including ζ potential, and polydispersity index (PDI) confirmed the formation of pure, stable monodisperse quasi-spherical oxide NPs of corresponding metals. The antimicrobial activity of biofabricated NPs was assessed against Gram-negative and Gram-positive bacteria, biofilm, yeast, mold, and algae via a well diffusion method. The results displayed significant antagonistic activity in comparison to their bulk and commercial antibiotics. Interestingly, the combined NPs exhibited promising synergistic biocide efficiency against examined pathogens which encourages their applications in adjuvant therapy and water/wastewater purification for controlling multiple drug-resistant microorganisms. To the best of our knowledge, no previous study reported the synthesis of semiconductor NPs by Proteus mirabilis and the biocide potency of combined NPs against a broad spectrum of pathogens not reported previously.

Thermal Calcination-Based Production of SnO₂ Nanopowder: An Analysis of SnO₂ Nanoparticle Characteristics and Antibacterial Activities

SnO₂ nanoparticle production using thermal treatment with tin(II) chloride dihydrate and polyvinylpyrrolidone capping agent precursor materials for calcination was investigated. Samples were analyzed using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), diffuse UV-vis reflectance spectra, photoluminescence (PL) spectra and the electron spin resonance (ESR). XRD analysis found tetragonal crystalline structures in the SnO₂ nanoparticles generated through calcination. EDX and FT-IR spectroscopy phase analysis verified the derivation of the Sn and O in the SnO₂ nanoparticle samples from the precursor materials. An average nanoparticle size of 4–15.5 nm was achieved by increasing calcination temperature from 500 °C to 800 °C, as confirmed through TEM. The valence state and surface composition of the resulting nanoparticle were analyzed using XPS. Diffuse UV-vis reflectance spectra were used to evaluate the optical energy gap using the Kubelka-Munk equation. Greater calcination temperature resulted in the energy band gap falling from 3.90 eV to 3.64 eV. PL spectra indicated a positive relationship between particle size and photoluminescence. Magnetic features were investigated through ESR, which revealed the presence of unpaired electrons. The magnetic field resonance decreases along with an increase of the g-factor value as the calcination temperature increased from 500 °C to 800 °C. Finally, Escherichia coli ATCC 25922 Gram (–ve) and Bacillus subtilis UPMC 1175 Gram (+ve) were used for in vitro evaluation of the tin oxide nanoparticle’s antibacterial activity. This work indicated that the zone of inhibition of 22 mm has good antibacterial activity toward the Gram-positive B. subtilis UPMC 1175.

Effect of sulfur source on photocatalytic degradation performance of CdS/MoS2 prepared with one-step hydrothermal synthesis

CdS/MoS₂, an extremely efficient photocatalyst, has been extensively used in hydrogen photoproduction and pollutant degradation. CdS/MoS₂ can be synthesized by a facile one-step hydrothermal process. However, the effect of the sulfur source on the synthesis of CdS/MoS₂via one-step hydrothermal methods has seldom been investigated. We report herein a series of one-step hydrothermal preparations of CdS/MoS₂ using three different sulfur sources: thioacetamide, l-cysteine, and thiourea. The results revealed that the sulfur source strongly affected the crystallization, morphology, elemental composition and ultraviolet (UV)-visible-light-absorption ability of the CdS/MoS₂. Among the investigated sulfur sources, thioacetamide provided the highest visible-light absorption ability for CdS/MoS₂, with the smallest average particle size and largest surface area, resulting in the highest efficiency in Methylene Blue (MB) degradation. The photocatalytic activity of CdS/MoS₂ synthesized from the three sulfur sources can be arranged in the following order: thioacetamide>l-cysteine>thiourea. The reaction rate constants (k) for thioacetamide, l-cysteine, and thiourea were estimated to be 0.0197, 0.0140, and 0.0084min^-1, respectively. However, thioacetamide may be limited in practical application in terms of its price and toxicity, while l-cysteine is relatively economical, less toxic and exhibited good photocatalytic degradation performance toward MB.

CTAB and SDS assisted facile fabrication of SnO2 nanoparticles for effective degradation of carbamazepine from aqueous phase: A systematic and comparative study of their degradation performance

In the present study, SnO₂ nanoparticles were successfully synthesized by chemical precipitation method using anhydrous aspartic acid and surfactant at two annealing temperatures, 300 °C and 600 °C. The effect of surfactants cationic CTAB and anionic SDS on the synthesized SnO₂ nanoparticles (NPs) were studied elaborately. In this article, for the first time, SnO₂ NPs were employed as an excellent photocatalyst in the degradation of carbamazepine (CBZ), a popular antiepileptic drug which is most commonly detected pharmaceutically active compounds (PhACs) in municipal wastewater under UV-C light irradiation. Comparative studies between the photocatalytic activity of SnO₂ NPs synthesized with CTAB (SC1) and SDS (SS1) on the degradation of the CBZ drug were investigated. Parameters like the effect of catalytic loading, initial concentration, pH and contact time were also studied for optimization. The results indicate that SC1 is a better photocatalyst with rate constant 6.66 × 10^-2 min^-1 than SS1 with rate 5.7 × 10^-2 min^-1. To determine the transformation product formed on the photodegradation LCMS (ESI) analysis was done. The synthesized SnO₂ NPs can be recycled up to 8th cycles without any notable alteration in its photocatalytic activity.

Polyol asserted hydrothermal synthesis of SnO2 nanoparticles for the fast adsorption and photocatalytic degradation of methylene blue cationic dye

Schematic representation of the photocatalytic degradation of MB dye using the SnO₂ nanocatalyst.

Phyto-synthesis and structural characterization of catalytically active gold nanoparticles biosynthesized using Delonix regia leaf extract

Biological methods of nanoparticles synthesis are ecologically sound and sustainable alternative to the conventional methods. On the basis of aforesaid premise, the present study deals with the optimization and fabrication of gold nanoparticles (Au-NPs) using easily available bio-resource, Delonix regia leaf extract. The use of practically nontoxic natural extracts and water allows the synthesis pathways presented to be considered as ‘‘green’’ and so permitting the synthesized Au-NPs to be used in sensitive areas, such as bioremediation. Various characterization techniques are adopted for the evaluation of size, stability, morphology, crystal nature, and purity of nanoparticles. Ultraviolet–visible spectroscopy analysis showed a surface Plasmon resonance peak for prepared Au-NPs at 542 nm, and its absorbance increased with increasing the interaction time. Transmission electron microscopy analysis showed that the particles were spherical and 4–24 nm in size. Energy dispersive X-ray spectroscopy analysis displayed a 2.2 keV peak corresponding to the pure phase gold nanocrystal. X-ray diffraction analysis proved the fabrication of crystalline Au-NPs with face-centered cubic geometry within 10 min. Furthermore, ζ potential (−15 mV) and Fourier transform infrared data suggested the role of polar polyphenolic compounds of leaf extract in fabrication and stabilization process. Biofabricated nanoparticles are demonstrated to have catalytic activity for the reduction of toxic nitro-organic pollutant o-nitroaniline. Therefore, the present study offers a straightforward, cost-efficient, eco-friendly, and sustainable alternative for the fabrication of catalytically active Au-NPs.

Studies on competitive adsorption of dyes onto carbon (XC-72) and regeneration of adsorbent

Carbon as an adsorbent has been widely studied for wastewater treatment, but the regeneration of adsorbent has been scarcely reported. In this paper, an economical and environmental method was applied to regenerate carbon (XC-72). Results showed that both anhydrous ethanol and deionized water did not obtain optimal effect for the desorption of Acid Orange 7, Ponceau 2R and Rhodamine B, but the desorption effect was dramatically improved when anhydrous ethanol and deionized water were mixed in a certain volume ratio. In addition, the adsorption kinetics of the three dyes were investigated, which showed that the process of adsorption could be well represented by the pseudo-second-order model. For the study of competitive adsorption, this indicated that the interaction between adsorbent and adsorbate had something to do with electrostatic attraction.