Preparation and Morphology Studies of Nano Zinc Oxide Obtained Using Native and Modified Chitosans

Nano zinc oxide (ZnO) with moderate surface area and high pore volume were prepared using a facile preparation method. Chitosan was utilized as both chelating and structure directing agent. The application of chitosans in this study suggested that even biowastes can be served in a productive manner economically. The surface modification of chitosan was carried out in order to increase the interaction between chitosan and zinc ions. The effect of sodium chloroacetate and isopropyl alcohol on the surface modification process was also explored. FT-IR (Fourier transform-infrared spectrometer) and TGA (Thermogravimetric analyses) analyses revealed that modified chitosans are more stable than those of unmodified chitosan. Among surface modified chitosans, CMC1 (1.5 M sodium chloroacetate and 75% isopropyl alcohol) showed enhanced surface properties. Freundlich adsorption isotherms as preliminary studies confirmed that modified chitosan showed enhanced interaction with zinc ions. The interaction of zinc salt with chitosans produced a zinc-chitosan polymer. This finally cleaved upon calcination to produce nano ZnO. The effects of different calcination temperatures indicated that 450 °C is the optimum calcination temperature to produce the nano ZnO with favored surface area (15.45 m²/g) and pore size (221.40 nm). SEM (Scanning electron microscope) and TEM (Transmission electron microscope) of ZnO indicated that uniform particle and shape distributions were obtained at low calcination temperature (450 °C).     

A Brief Photocatalytic Study of ZnO Containing Cerium towards Ibuprofen Degradation

Ibuprofen (IBU) is one of the most-sold anti-inflammatory drugs in the world, and its residues can reach aquatic systems, causing serious health and environmental problems. Strategies are used to improve the photocatalytic activity of zinc oxide (ZnO), and thosethat involvethe inclusion of metalhave received special attention. The aim of this work was to investigate the influence of the parameters and toxicity of a photoproduct using zinc oxide that contains cerium (ZnO-Ce) for the photodegradation of ibuprofen. The parameters include the influence of the photocatalyst concentration (0.5, 0.5, and 1.5 g L⁻¹) as well as the effects of pH (3, 7, and 10), the effect of H₂O₂, and radical scavengers. The photocatalyst was characterized by Scanning Electron Microscopy-Energy Dispersive Spectroscopy, Transmission electron microscopy, Raman, X-Ray Diffraction, surface area, and diffuse reflectance. The photocatalytic activity of ibuprofen was evaluated in an aqueous solution under UV light for 120 min. The structural characterization by XRD and SEM elucidated the fact that the nanoparticle ZnO contained cerium. The band gap value was 3.31 eV. The best experimental conditions for the photodegradation of IBU were 60% obtained in an acidic condition using 0.50 g L⁻¹ of ZnO-Ce in a solution of 20 ppm of IBU. The presence of hydrogen peroxide favored the photocatalysis process. ZnO-Ce exhibited good IBU degradation activity even after three photocatalytic cycles under UV light. The hole plays akey role in the degradation process of ibuprofen. The toxicity of photolyzed products was monitored against Artemia salina (bioindicator) and did not generate toxic metabolites. Therefore, this work provides a strategic design to improve ZnO-Ce photocatalysts for environmental remediation.     

A High-Efficiency TiO2/ZnO Nano-Film with Surface Oxygen Vacancies for Dye Degradation

Photocatalytic degradation of organic pollutants in water is a highly efficient and green approach. However, the low quantum efficiency is an intractable obstacle to lower the photocatalytic efficiency of photocatalysts. Herein, the TiO₂/ZnO heterojunction thin films combined with surface oxygen vacancies (OVs) were prepared through magnetron sputtering, which was designed to drive rapid bulk and surface separation of charge carriers. The morphology and structural and compositional properties of films were investigated via different techniques such as SEM, XRD, Raman, AFM, and XPS. It has been found that by controlling the O₂/Ar ratio, the surface morphology, thickness, chemical composition, and crystal structure can be regulated, ultimately enhancing the photocatalytic performance of the TiO₂/ZnO heterostructures. In addition, the heterojunction thin film showed improved photocatalytic properties compared with the other nano-films when the outer TiO₂ layer was prepared at an O₂/Ar ratio of 10:35. It degraded 88.0% of Rhodamine B (RhB) in 90 min and 90.8% of RhB in 120 min. This was attributed to the heterojunction interface and surface OVs, which accelerated the separation of electron–hole (e–h) pairs.     

Synthesis of Selected Mixed Oxide Materials with Tailored Photocatalytic Activity in the Degradation of Tetracycline

The elimination of antibiotics occurring in the natural environment has become a great challenge in recent years. Among other techniques, the photocatalytic degradation of this type of pollutant seems to be a promising approach. Thus, the search for new photoactive materials is currently of great importance. The present study concerns the sol–gel synthesis of mono, binary and ternary TiO₂-based materials, which are used as active photocatalysts. The main goal was to evaluate how the addition of selected components—zirconium dioxide (ZrO₂) and/or zinc oxide (ZnO)—during the synthesis of TiO₂-based materials and the temperature of thermal treatment affect the materials’ physicochemical and photocatalytic properties. The fabricated mixed oxide materials underwent detailed physicochemical analysis, utilizing scanning-electron microscopy (SEM), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), energy-dispersive X-ray spectroscopy (EDS), low-temperature N₂ sorption (BET model), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The synthesized mixed oxide materials were used as photocatalysts in the heterogeneous photodegradation of tetracycline (TC). The physicochemical properties of the fabricated photocatalysts, including morphology, crystalline and textural structure, as well as the pH of the reaction system in the photocatalytic tests, were taken into account in determining their photo-oxidation activity. LC–MS/MS analysis was used to identify the possible degradation products of the selected antibiotic.     

Growth of High-Density Zinc Oxide Nanorods on Porous Silicon by Thermal Evaporation

The formation of high-density zinc oxide (ZnO) nanorods on porous silicon (PS) substrates at growth temperatures of 600–1000 °C by a simple thermal evaporation of zinc (Zn) powder in the presence of oxygen (O₂) gas was systematically investigated. The high-density growth of ZnO nanorods with (0002) orientation over a large area was attributed to the rough surface of PS, which provides appropriate planes to promote deposition of Zn or ZnO_x seeds as nucleation sites for the subsequent growth of ZnO nanorods. The geometrical morphologies of ZnO nanorods are determined by the ZnO_x seed structures, i.e., cluster or layer structures. The flower-like hexagonal-faceted ZnO nanorods grown at 600 °C seem to be generated from the sparsely distributed ZnO_x nanoclusters. Vertically aligned hexagonal-faceted ZnO nanorods grown at 800 °C may be inferred from the formation of dense arrays of ZnO_x clusters. The formation of disordered ZnO nanorods formed at 1000 °C may due to the formation of a ZnO_x seed layer. The growth mechanism involved has been described by a combination of self-catalyzed vapor-liquid-solid (VLS) and vapor-solid (VS) mechanism. The results suggest that for a more precise study on the growth of ZnO nanostructures involving the introduction of seeds, the initial seed structures must be taken into account given their significant effects.     

Application of Photocatalytic Concrete Paving Blocks in Poland—Verification of Effectiveness of Nitric Oxides Reduction and Novel Test Method

Photocatalytic concrete is one of the most promising concrete technologies of the past decades. Application of nanometric TiO₂ to cement matrices enables the reduction of harmful airborne pollutants. Although a number of implementations of this technology are described in this paper, problems related to test conditions are also reported. One major issue is the sufficient light irradiation that for higher latitudes can be significantly reduced. In this paper, a field campaign on the implementation of photocatalytic concrete pavement in Warsaw (52.23° N) is briefly described. Based on experience from the field campaign, a novel test method is developed. In the research, the effectiveness of nitric oxide reduction is verified at natural light irradiation for various dates of solar position at noon in central Poland (51.83° N). The results confirm the benefits of using photocatalytic materials at higher latitudinal locations. The experimental setup presented in the study combines the advantages of controlled measurement conditions typical in laboratory tests with the possibility of including natural sunlight conditions in the investigation process.     

Preparation of “Cauliflower-Like” ZnO Micron-Sized Particles

Porous polydivinyl benzene (PDVB) microspheres of narrow size distribution were formed by a single-step swelling process of template uniform polystyrene microspheres with divinyl benzene (DVB), followed by polymerization of the DVB within the swollen template microspheres. The PDVB porous particles were then formed by dissolution of the template polystyrene polymer. Unique “cauliflower-like” ZnO microparticles were prepared by the entrapping of the ZnO precursor ZnCl₂ in the PDVB porous microspheres under vacuum, followed by calcination of the obtained ZnCl₂-PDVB microspheres in an air atmosphere. The morphology, crystallinity and fluorescence properties of those ZnO microparticles were characterized. This “cauliflower-like” shape ZnO particles is in contrast to a previous study demonstrated the preparation of spherical shaped porous ZnO and C-ZnO microparticles by a similar method, using zinc acetate (ZnAc) as a precursor. Two diverted synthesis mechanisms for those two different ZnO microparticles structures are proposed, based on studies of the distribution of each of the ZnO precursors within the PDVB microspheres.     

Zinc Oxide Nanoparticles for Water Purification

In this study, zinc oxide nanoparticles were synthesized through a simple co-precipitation method starting from zinc acetate dihydrate and sodium hydroxide as reactants. The as-obtained ZnO nanoparticles were morphologically and structurally characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photocatalytic activity, and by determining the antimicrobial activity against Gram-negative and Gram-positive bacteria. The XRD pattern of the zinc oxide nanoparticles showed the wurtzite hexagonal structure, and its purity highlighted that the crystallinity correlated with the presence of a single product, zinc oxide. The ZnO nanoparticles have an average crystallite size of 19 ± 11 nm, which is in accordance with the microscopic data. ZnO nanoparticles were tested against methyl orange, used as a model pollutant, and it was found that they exhibit strong photocatalytic activity against this dye. The antibacterial activity of ZnO nanoparticles was tested against Gram-negative and Gram-positive strains (Escherichia coli, Staphylococcus aureus, and Candida albicans). The strongest activity was found against Gram-positive bacteria (S. aureus).     

Economic Friendly ZnO-Based UV Sensors Using Hydrothermal Growth: A Review

Ultraviolet (UV) sensors offer significant advantages in human health protection and environmental pollution monitoring. Amongst various materials for UV sensors, the zinc oxide (ZnO) nanostructure is considered as one of the most promising candidates due to its incredible electrical, optical, biomedical, energetic and preparing properties. Compared to other fabricating techniques, hydrothermal synthesis has been proven to show special advantages such as economic cost, low-temperature process and excellent and high-yield production. Here, we summarize the latest progress in research about the hydrothermal synthesis of ZnO nanostructures for UV sensing. We particularly focus on the selective hydrothermal processes and reveal the effect of key factors/parameters on ZnO architectures, such as the laser power source, temperature, growth time, precursor, seeding solution and bases. Furthermore, ZnO hydrothermal nanostructures for UV applications as well as their mechanisms are also summarized. This review will therefore enlighten future ideas of low-temperature and low-cost ZnO-based UV sensors.     

Performance Evaluation of Ultra-Violet Light and Iron Oxide Nanoparticles for the Treatment of Synthetic Petroleum Wastewater: Kinetics of COD Removal

In this study, the use of ultra-violet (UV) light with or without iron oxide nanoparticles (IONPs) for the degradation of synthetic petroleum wastewater was investigated. The IONPs was synthesised by sodium borohydride reduction of ferric chloride solution and was characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), x-ray fluorescence spectrophotometry (XRF), and energy dispersive spectroscopy (EDS). The amount of degradation was evaluated by chemical oxygen demand (COD) determination. Experimental results show that the COD removal from synthetic petroleum wastewater by IONPs/UV system was more effective than they were independently. The combination of UV light at a wavelength of 254 nm, pH of 8, and 1.0 g of IONPs resulted in COD removal from 10.5% up to 95.5%. The photocatalytic degradation of synthetic petroleum wastewater is about 1.3–2.0 times faster in comparison to UV light only. The removal of COD from synthetic petroleum wastewater by UV light and IONPs follows the pseudo-first-order kinetic model with rate constant k ranging from 0.0133 min⁻¹ to 0.0269 min⁻¹. Consequently, this study has shown that the use of UV light in the presence of IONPs is favourable and effective for the removal of organic pollutants from petroleum refinery wastewater.     

Construction of TiO2-Eggshell for Efficient Degradation of Tetracycline Hydrochloride: Sunlight Induced In-Situ Formation of Carbonate Radical

Photocatalytic degradation of an antibiotic by utilizing inexhaustible solar energy represents an ideal solution for tackling global environment issues. The target generation of active oxidative species is highly desirable for the photocatalytic pollutants degradation. Herein, aiming at the molecular structure of tetracycline hydrochloride (TC), we construct sunlight-activated high-efficient catalysts of TiO₂-eggshell (TE). The composite ingeniously utilizes the photoactive function of TiO₂ and the composition of eggshell, which can produce oxidative ·CO₃⁻ species that are especially active for the degradation of aromatic compounds containing phenol or aniline structures. Through the synergistic oxidation of the··CO₃⁻ with the traditional holes (h⁺), superoxide radicals (·O²⁻) and hydroxyl radicals (·OH) involved in the photocatalytic process, the optimal TE photocatalyst degrades 92.0% TC in 30 min under solar light, which is higher than TiO₂ and eggshell. The photocatalytic degradation pathway of TC over TE has been proposed. The response surface methodology is processed by varying four independent parameters (TC concentration, pH, catalyst dosage and reaction time) on a Box–Behnken design (BBD) to optimize the experimental conditions. It is anticipated that the present work can facilitate the development of novel photocatalysts for selective oxidation based on ·CO₃⁻.     

Decoration of Zinc Oxide Nanorods into the Surface of Activated Carbon Obtained from Agricultural Waste for Effective Removal of Methylene Blue Dye

Zinc oxide (ZnO) nanorods incorporated activated carbon (AC) composite photocatalyst was synthesized using a hydrothermal process. The AC was prepared from lapsi (Choerospondias axillaris) seed stone, an agricultural waste product, found in Nepal by the chemical activation method. An aqueous suspension of AC with ZnO precursor was subjected to the hydrothermal treatment at 140 °C for 2 h to decorate ZnO rods into the surface of AC. As-obtained ZnO nanorods decorated activated carbon (ZnO/AC) photocatalyst was characterized by various techniques, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. Results showed that highly crystalline hexagonal ZnO nanorods were effectively grown on the surface of porous AC. The photocatalytic property of the as-prepared ZnO/AC composite was studied by degrading methylene blue (MB) dye under UV-light irradiation. The ZnO/AC composite showed better photocatalytic property than that of the pristine ZnO nanorods. The enhanced photocatalytic performance in the case of the ZnO/AC composite is attributed to the combined effects of ZnO nanorods and AC.     

Indium Doped Zinc Oxide Thin Films Deposited by Ultrasonic Chemical Spray Technique,Starting from Zinc Acetylacetonate and Indium Chloride

The physical characteristics of ultrasonically sprayed indium-doped zinc oxide (ZnO:In) thin films, with electrical resistivity as low as 3.42 × 10⁻³ Ω·cm and high optical transmittance, in the visible range, of 50%–70% is presented. Zinc acetylacetonate and indium chloride were used as the organometallic zinc precursor and the doping source, respectively, achieving ZnO:In thin films with growth rate in the order of 100 nm/min. The effects of both indium concentration and the substrate temperature on the structural, morphological, optical, and electrical characteristics were measured. All the films were polycrystalline, fitting well with hexagonal wurtzite type ZnO. A switching in preferential growth, from (002) to (101) planes for indium doped samples were observed. The surface morphology of the films showed a change from hexagonal slices to triangle shaped grains as the indium concentration increases. Potential applications as transparent conductive electrodes based on the resulting low electrical resistance and high optical transparency of the studied samples are considered.     

Enhanced Photocatalytic Efficiency of N–F-Co-Embedded Titania under Visible Light Exposure for Removal of Indoor-Level Pollutants

N–F-co-embedded titania (N–F–TiO₂) photocatalysts with varying N:F ratios were synthesized and tested for their ability to photocatalyze the degradation of pollutants present at indoor air levels using visible light. The synthesis was achieved using a solvothermal process with tetrabutyl titanate, urea and ammonium fluoride as sources of Ti, N and F, respectively. Three selected volatile organic compounds (toluene, ethyl benzene and o-xylene) were selected as the test pollutants. The prepared composites were characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Ultra-violet (UV)-visible spectroscopy. The photocatalytic degradation efficiencies of N–F–TiO₂ composites were higher than those obtained using pure TiO₂ and N–TiO₂. Moreover, these efficiencies increased as the N:F ratio decreased from sixteen to eight, then decreased as it dropped further to three, indicating the presence of an optimal N:F ratio. Meanwhile, as retention time decreased from 12.4 to 0.62 s, the average photocatalytic efficiencies decreased from 65.4% to 21.7%, 91.5% to 37.8% and 95.8% to 44.7% for toluene, ethyl benzene and o-xylene, respectively. In contrast, the photocatalytic reaction rates increased as retention time decreased. In consideration of all of these factors, under optimized operational conditions, the prepared N–F–TiO₂ composites could be utilized for the degradation of target pollutants at indoor air levels using visible light.     

Sustainable Production of Arecanut Husk Ash as Potential Silica Replacement for Synthesis of Silicate-Based Glass-Ceramics Materials

Arecanut husk (AH) was selected as a material for silica replacement in the synthesis process of glass-ceramics zinc silicate and also the fact that it has no traditional use and often being dumped and results in environmental issues. The process of pyrolysis was carried out at temperature 700 °C and above based on thermogravimetric analysis to produce arecanut husk ash (AHA). The average purity of the silica content in AHA ranged from 29.17% to 45.43%. Furthermore, zinc oxide was introduced to AHA and zinc silicate started to form at sintering temperature 700 °C and showed increased diffraction intensity upon higher sintering temperature of 600 °C to 1000 °C based on X-ray diffraction (XRD) analysis. The grain sizes of the zinc silicate increased from 1011 nm to 3518 nm based on the morphological studies carried out by field emission scanning electron microscopy (FESEM). In addition, the optical band gap of the sample was measured to be in the range from 2.410 eV to 2.697 eV after sintering temperature. From the data, it is believed that a cleaner production of low-cost zinc silicate can be achieved by using arecanut husk and have the potential to be used as phosphors materials.     

Iron Oxide Silica Derived from Sol-Gel Synthesis

In this work we investigate the effect of iron oxide embedded in silica matrices as a function of Fe/Si molar ratio and sol pH. To achieve homogeneous dispersion of iron oxide particles, iron nitrate nonahydrate was dissolved in hydrogen peroxide and was mixed with tetraethyl orthosilicate and ethanol in a sol-gel synthesis method. Increasing the calcination temperature led to a reduction in surface area, although the average pore radius remained almost constant at about 10 Å, independent of the Fe/Si molar ratio or sol pH. Hence, the densification of the matrix was accompanied by similar reduction in pore volume. However, calcination at 700 °C resulted in samples with similar surface area though the iron oxide content increased from 5% to 50% Fe/Si molar ratio. As metal oxide particles have lower surface area than polymeric silica structures, these results strongly suggest that the iron oxides opposed the silica structure collapse. The effect of sol pH was found to be less significant than the Fe/Si molar ratio in the formation of molecular sieve structures derived from iron oxide silica.     

Improving Photocatalytic Performance Using Nanopillars and Micropillars

A recent research emphasis has been placed on the development of highly crystallized nanostructures as a useful technology for many photocatalytic applications. With the unique construction of semiconductor transition metal oxide nanostructures in the form of nanopillars—artificially designed pillar-shaped structures grouped together in lattice-type arrays—the surface area for photocatalytic potential is increased and further enhanced through the introduction of dopants. This short review summarizes the work on improving the efficiency of photocatalyst nanopillars through increased surface area and doping within the applications of water splitting, removal of organic pollutants from the environment, photoswitching, soot oxidation, and photothermalization.     

Black TiOx Films with Photothermal-Assisted Photocatalytic Activity Prepared by Reactive Sputtering

Titanium oxide is widely applied as a photocatalyst. However, its low efficiency and narrow light absorption range are two main disadvantages that severely impede its practical application. In this work, black TiO_x films with different chemical compositions were fabricated by tuning target voltage and controlling O₂ flow during reactive DC magnetron sputtering. The optimized TiO_x films with mixed phases (TiO, Ti₂O₃, Ti₃O₅, and TiO₂) exhibited fantastic photothermal and photocatalytic activity by combining high light-absorptive Ti₂O₃ and Ti₃O₅ phases with the photocatalytic TiO₂ phase. The sample prepared with oxygen flow at 5.6 ± 0.2 sccm and target voltage near 400 V exhibited excellent optical absorbance of 89.29% under visible light, which could improve surface temperature to 114 °C under sunlight. This film could degrade Rhodamine-B up to 74% after 150 min of UV irradiation. In a word, this work provides a guideline for fabricating black TiO_x films with photothermal-assisted photocatalytic activity by reactive DC magnetron sputtering, which could avoid the usage of hydrogen and is convenient for quantity preparation.     

One Step In-Situ Synthesis of Zinc Oxide Nanoparticles for Multifunctional Cotton Fabrics

Zinc oxide nanoparticles (ZnO NPs) have acquired great significance in the textile sector due to their impressive efficiency and multifold utilization, such as antimicrobials, UV protection, photo catalytic activity, and self-cleaning. The aim of this work is in-situ growth of ZnO NPs on 100% cotton fabrics with the one-step hydrothermal method for preparation of multifunctional textile with UV protecting, antibacterial, and photo catalytic properties. Sodium hydroxide (NaOH) and Zinc nitrate hexahydrate [Zn(NO₃)₂·6H₂O] were used as reactants for the growth of zinc oxide on the 100% cotton fabrics. The loaded amount of Zn contents on the cotton fabric was determined by using induced coupled plasma atomic emission spectroscopy (ICP-AES). The surface morphological characterization of deposited ZnO NPs was examined, employing scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and, Fourier- transform infrared spectroscopy (FTIR). The characterization results showed the presence of ZnO NPs on cotton fabrics having hexagonal wurtzite crystalline structure. The synthesized ZnO NPs on fabrics exhibited promising results for antibacterial, UV protection, and photo catalytic performance.     

Efficiency Enhancement of Dye-Sensitized Solar Cells’ Performance with ZnO Nanorods Grown by Low-Temperature Hydrothermal Reaction

In this study, aligned zinc oxide (ZnO) nanorods (NRs) with various lengths (1.5–5 µm) were deposited on ZnO:Al (AZO)-coated glass substrates by using a solution phase deposition method; these NRs were prepared for application as working electrodes to increase the photovoltaic conversion efficiency of solar cells. The results were observed in detail by using X-ray diffraction, field-emission scanning electron microscopy, UV-visible spectrophotometry, electrochemical impedance spectroscopy, incident photo-to-current conversion efficiency, and solar simulation. The results indicated that when the lengths of the ZnO NRs increased, the adsorption of D-719 dyes through the ZnO NRs increased along with enhancing the short-circuit photocurrent and open-circuit voltage of the cell. An optimal power conversion efficiency of 0.64% was obtained in a dye-sensitized solar cell (DSSC) containing the ZnO NR with a length of 5 µm. The objective of this study was to facilitate the development of a ZnO-based DSSC.