Photocatalytic paper using zinc oxide nanorods

ZnO nanostructures: synthesis by anodization and applications in photoelectrocatalysis

Solar energy is a clean and abundant energy source. In a photoelectrochemical cell, energy from sunlight is captured and converted into electric power, chemical fuels such as hydrogen is employed to degrade organic pollutants. ZnO is a promising material for photoelectrocatalysis due to its remarkable properties. The aim of this review is to perform an exhaustive revision of nanostructured ZnO synthesis by electrochemical anodization in order to control surface characteristics of this material through anodization parameters such as electrolyte type and concentration, potential, time, temperature, stirring, and post treatment. Finally, application of ZnO nanostructures is overviewed to observe how surface characteristics affected the ZnO photoelectrocatalytic performance.

Metal Oxide-Based Photocatalytic Paper: A Green Alternative for Environmental Remediation

The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and N2 reductions, and microorganism inactivation. However, to maintain its eco-friendly aspect, new solutions must be identified to ensure sustainability. One alternative is creating an enhanced photocatalytic paper by introducing cellulose-based materials to the process. Paper can participate as a substrate for the metal oxides, but it can also form composites or membranes, and it adds a valuable contribution as it is environmentally friendly, low-cost, flexible, recyclable, lightweight, and earth abundant. In term of photocatalysts, the use of metal oxides is widely spread, mostly since these materials display enhanced photocatalytic activities, allied to their chemical stability, non-toxicity, and earth abundance, despite being inexpensive and compatible with low-cost wet-chemical synthesis routes. This manuscript extensively reviews the recent developments of using photocatalytic papers with nanostructured metal oxides for environmental remediation. It focuses on titanium dioxide (TiO2) and zinc oxide (ZnO) in the form of nanostructures or thin films. It discusses the main characteristics of metal oxides and correlates them to their photocatalytic activity. The role of cellulose-based materials on the systems’ photocatalytic performance is extensively discussed, and the future perspective for photocatalytic papers is highlighted.

Preparation of visible light-responsive photocatalytic paper containing BiVO4@diatomite/MCC/PVBCFs for degradation of organic pollutants

Combining adsorption and photocatalysis is an effective strategy for degrading organic pollutants. Here, BiVO₄@diatomite composite photocatalyst (BiVO₄@diatomite CP) was prepared by hydrothermal synthesis from Bi(NO₃)₃·5H₂O glycerin solution, NH₄VO₃ solution and diatomite. BiVO₄@diatomite/microcrystalline cellulose/PVB composite fibers (BiVO₄@diatomite/MCC/PVBCFs) were prepared from BiVO₄@diatomite CPs, microcrystalline cellulose (MCC) and PVB ethanol solution using the electrospinning method. BiVO₄@diatomite/MCC/PVBCFs were then mixed with pulp fibers to prepare the visible light-responsive photocatalytic paper. BiVO₄@diatomite CP with a BiVO₄/diatomite ratio of 6:4 had good interface states and displayed good photocatalytic activity with 64.32% degradation of methylene blue (MB) after 4 h. A PVB ethanol solution (6%) was formulated with BiVO₄@diatomite CP and MCC to provide an ethanol spinning solution (12% solid) to prepare BiVO₄@diatomite/MCC/PVBCFs (3:3:4). The resulting fibers had smooth surfaces, compact structures and exhibited good photocatalytic activity (66.80% and 56.80% degradation of MB and formaldehyde (HCHO), respectively, after 4 h). Photocatalytic paper containing 18% BiVO₄@diatomite/MCC/PVBCFs had good photocatalytic activity with 50.20% degradation of HCHO after 4 h. This paper also had good physical properties and has the potential to be used for the photocatalytic degradation of indoor air pollutants, such as HCHO.

Growth Mechanism of Sea Urchin ZnO Nanostructures in Aqueous Solutions and Their Photocatalytic Activity for the Degradation of Organic Dyes

This work reports the development of a fast and simple route for the synthesis of ZnO sea urchin (SU) nanostructures by the formation and assembly of ZnO nanorods under favorable growth conditions in an aqueous solution. The thermal treatment of a basic zinc acetate solution in ethanol results in the formation of aggregated seed clusters consisting of small ZnO nanorods, which were then grown in a precursor solution containing Zn(NO₃)₂·6H₂O and hexamethylenetetramine to assemble the SU structures from the anisotropic ZnO nanorods on the surface of the seed clusters. Each ZnO nanoparticle in the aggregated seed clusters grew sequentially into a ZnO nanorod, and the nanorods were concentric to the core of the clusters yielding the unique SU-like shape. In the presence of a capping agent such as cetyl trimethyl ammonium bromide (CTAB), the aggregated seed clusters were not formed, and the growth of the CTAB-capped ZnO nanorods resulted in separated rods with average aspect ratios of ∼10. The SU ZnO nanostructures exhibit a hexagonal wurtzite crystal structure and higher specific surface area (26.9 m²/g) than the CTAB-capped nanorods (17.7 m²/g). The SU ZnO nanostructures show superior photocatalytic efficiency for the degradation of three common organic dyes compared to the ZnO nanorods. The removal efficiencies of indigo carmine, methylene blue, and rhodamine B by the SU nanostructures were 99, 86, and 96%, respectively, after 1 h of UV irradiation. Therefore, the ZnO SU structures have the potential to be a versatile photocatalyst for the photodegradation of organic dyes in industrial wastewater.

Flexible Photocatalytic Paper with Cu2O and Ag Nanoparticle-Decorated ZnO Nanorods for Visible Light Photodegradation of Organic Dye

We report on the fabrication of flexible photocatalytic paper comprised of Cu₂O and Ag nanoparticle (NP)-decorated ZnO nanorods (NRs) and its application in visible light photodegradation of organic dye. ZnO NRs are first grown on a kraft paper substrate using a hydrothermal method. The NRs are subsequently decorated with Cu₂O, Ag, or both NPs formed by photoreduction processes. Scanning electron microscopy and X-ray diffraction analysis confirm the crystallinity of ZnO NRs. Transmission electron microscopy analysis confirms the compositions of the two types of NPs. Four different types of photocatalytic papers with a size of 10 × 10 cm² are prepared and used to degrade a 10-μM and 100-mL rhodamine B solution. The paper with Cu₂O and Ag NP-co-decorated ZnO NRs has the best efficiency with first-order kinetic constants of 0.017 and 0.041 min^-1 under the illumination of a halogen lamp and direct sunlight, respectively. The performance of the photocatalytic paper compares well with other substrate-supported ZnO nanocomposite photocatalysts. With the advantages of flexibility, light weight, nontoxicity, low cost, and ease of fabrication, the photocatalytic paper has good potential for visible light photocatalysis.

The direct-writing of low cost paper based flexible electrodes and touch pad devices using silver nano-ink and ZnO nanoparticles

We report a novel and simple approach for the synthesis of silver nanoparticles capped with inositol (Ag NPs/Ino) by the reduction of silver salt with ascorbic acid under basic conditions. UV-vis, TEM, FTIR and TGA techniques were used to characterize the Ag NPs/Ino to determine the size, shape and surface modification of the NPs. Stable silver nano-ink was prepared in aqueous solution containing 1% PVP (stabilizer) and glycerol (cosolvent) and was used for the direct-writing of a paper electrode with a roller ball-point pen for electrochemical applications. The solvent, stabilizing agents, concentration of NPs (10%), paper substrate, sintering temperature (40 °C) and sintering time (15 min) were optimized to obtain a uniform coating of Ag NPs on the paper substrate. Further, the synthesis and fabrication of ZnO NPs on a paper substrate was put forward to design a touch pad device based on the piezoelectric effect. The preparation of paper based devices suggests a direction for the development of a simple, low cost and compatible approach for the direct-writing of paper based flexible electrodes and electronics for future applications.

Synthesis of N-doped ZnO nanoparticles with cabbage morphology as a catalyst for the efficient photocatalytic degradation of methylene blue under UV and visible light

In this study, the synthesis of nitrogen-doped zinc oxide nanoparticles with a cabbage like morphology (N-ZnONCBs) by a hydrothermal method using zinc acetate dihydrate as a precursor and hydrazine monohydrate as a nitrogen source is reported. N-ZnONCB were characterized using UV-visible Spectroscopy (UV-Vis), Fluorescence Spectroscopy, Fourier Transmittance Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Dispersive Spectroscopy (EDS) and EDX elemental mapping. N-ZnONCBs were tested for their photocatalytic capabilities in the degradation of methylene blue (MB) under UV-light and visible light irradiation for about 0 to 80 minutes and 0 to 50 min respectively. The N-ZnONCB catalyst demonstrated improved photodegradation efficiency (98.6% and 96.2%) and kinetic degradation rates of MB (k = −0.0579 min⁻¹ and k = −0.0585 min⁻¹) under UV light and visible light irradiation at different time intervals. The photodegradation study was also evaluated with different dosages of N-ZnONCB catalyst, different initial concentrations of MB and variation in the pH (3, 5, 9 and 11) of the solution of MB under UV light and visible light irradiation. The photocatalytic degradation intermediate products were obtained by liquid chromatography mass spectra (LC-MS) and also complete mineralization was determined by using Total Organic Carbon (TOC) studies. This photocatalyst was also tested with 2,4-dichlorophenol (2,4-DCP) under visible light irradiation at different time intervals. Fluorescence and quenching studies were performed for the binding interaction between the N-ZnONCB catalyst and MB dye. A Zetasizer was used to find the charge and average size of the N-ZnONCB catalyst and also the charge of the N-ZnONCB catalyst before and after MB dye solution adsorption. The N-ZnONCB catalyst was also tested for its photostability and reusability with a percentage degradation rate of MB (93.2%) after 4 cycle experiments. These results have clearly demonstrated that the N-ZnONCB catalyst can be applied for the photocatalytic degradation of MB from wastewater samples.

In this study, the synthesis of nitrogen-doped zinc oxide nanoparticles with a cabbage like morphology (N-ZnONCBs) by a hydrothermal method using zinc acetate dihydrate as a precursor and hydrazine monohydrate as a nitrogen source is reported.

Zinc oxide nano-enabled microfluidic reactor for water purification and its applicability to volatile organic compounds

This paper reports fast and efficient chemical decontamination of water within a tree-branched centimeter-scale microfluidic reactor. The microreactor integrates Zinc oxide nanowires (ZnO NWs) in situ grown acting as an efficient photocatalytic nanomaterial layer. Direct growth of ZnO NWs within the microfluidic chamber brings this photocatalytic medium at the very close vicinity of the water flow path, hence minimizing the required interaction time to produce efficient purification performance. We demonstrate a degradation efficiency of 95% in <5 s of residence time in one-pass only. According to our estimates, it becomes attainable using microfluidic reactors to produce decontamination of merely 1 l of water per day, typical of the human daily drinking water needs. To conduct our experiments, we have chosen a laboratory-scale case study as a seed for addressing the health concern of water contamination by volatile organic compounds (VOCs), which remain difficult to remove using alternative decontamination techniques, especially those involving water evaporation. The contaminated water sample contains mixture of five pollutants: Benzene; Toluene; Ethylbenzene; m–p Xylenes; and o-Xylene (BTEX) diluted in water at 10 p.p.m. concentration of each. Degradation was analytically monitored in a selective manner until it falls below 1 p.p.m. for each of the five pollutants, corresponding to the maximum contaminant level (MCL) established by the US Environmental Protection Agency (EPA). We also report on a preliminary study, investigating the nature of the chemical by-products after the photocatalytic VOCs degradation process.

Review of recent research on flexible multifunctional nanopapers

Traditional paper and papermaking have struggled with a declining market during the last few decades. However, the incorporation of nanotechnology into papermaking has brought possibilities to develop low-cost, biocompatible and flexible products with sophisticated functionalities. The functionality of nanopapers emerges from the intrinsic properties of the nanofibrous network, the additional loading of specific nanomaterials (NMs), or the additional deposition and patterning of thin films of nanomaterials on the paper surface. A successful development of functional nanopapers requires understanding how the nanopaper matrix, nanofillers, nanocoating pigments, nanoprinting inks, processing additives and manufacturing processes all interact to provide the intended functionality. This review addresses the emerging area of functional nanopapers. This review discusses flexible and multifunctional nanopapers, NMs being used in nanopaper making, manufacturing techniques, and functional applications that provide new important possibilities to utilize papermaking technology. The interface where NM research meets traditional papermaking has important implications for food packaging, energy harvesting and energy storage, flexible electronics, low-cost devices for medical diagnostics, and numerous other areas.

Synthesis of hybrid paper sheets with enhanced air barrier and antimicrobial properties for food packaging

Paper sheets made from bagasse pulp have been modified using nanocellulose (NC) obtained from the same raw material. Modification of paper sheets have been carried out either through loading of paper with different concentrations of NC and antibacterial agent, Chitosan (Ch) during making sheets, or by surface coating of the paper. Crystals of NC extracted using concentrated sulfuric acid from bagasse pulp were found to have crystallinity index (CrI) 90%. Morphology of obtained NC has been confirmed by TEM and images revealed formation of NC crystals with large size distribution ranges from 4 to 60nm. Mechanical properties and air permeability of paper sheets loaded with different ratios of NC and Ch have been investigated. The results showed that presence of NC did not negatively affect the obtained modified paper sheets, while air permeability decreased with adding 8% NC to paper matrix. On the other hand, surface coverage of paper sheets with NC greatly reduced air permeability. Antimicrobial investigations carried out by optical density method indicated that presence of Ch in the paper sheets as an additive or in a coating formulation enhanced paper resistance to different microorganisms especially those causing food poisoning. The current study confirms that the modified paper can have potential application in food packaging.

Anti-microbial surfaces: An approach for deposition of ZnO nanoparticles on PVA-Gelatin composite film by screen printing technique

Initially micro-organisms get exposed to the surfaces, this demands development of anti-microbial surfaces to inhibit their proliferation. Therefore, herein, we attempt screen printing technique for development of PVA-GE/ZnO nanocomposite (PG/ZnO) films. The synthesis of PG/ZnO nanocomposite includes two steps as: (i) Coating of Zinc Oxide nanoparticles (ZnO NPs) by poly ethylene glycol in order to be compatible with organic counterparts. (ii) Deposition of coated nanoparticles on the PG film surface. The results suggest the enhancement in anti-microbial activity of PG/ZnO nanocomposite over pure ZnO NPs against both Gram positive Bacillus subtilis and Gram negative Escherichia coli from zone of inhibition. The uniformity in deposition is further confirmed by scanning electron microscopy (SEM) images. The phase identification of ZnO NPs and formation of PG/ZnO nanocomposite has been confirmed by X-ray diffraction (XRD) analysis and UV-vis spectroscopy (UV-vis). The Attenuated total reflection Spectroscopy (ATR) analysis indicates the ester bond between PVA and gelatin molecules. The thermal stability of nanocomposite is studied by thermogravimetric analysis (TGA) revealing increase in crystallinity due to ZnO NPs which could be utilized to inhibit the growth of micro-organisms. The tensile strength is found to be higher and percent elongation is double of PG/ZnO nanocomposite than PG composite film.

Self-decontaminating photocatalytic zinc oxide nanorod coatings for prevention of marine microfouling: a mesocosm study

The antifouling (AF) properties of zinc oxide (ZnO) nanorod coated glass substrata were investigated in an out-door mesocosm experiment under natural sunlight (14:10 light: dark photoperiod) over a period of five days. The total bacterial density (a six-fold reduction) and viability (a three-fold reduction) was significantly reduced by nanocoatings in the presence of sunlight. In the absence of sunlight, coated and control substrata were colonized equally by bacteria. MiSeq Illumina sequencing of 16S rRNA genes revealed distinct bacterial communities on the nanocoated and control substrata in the presence and absence of light. Diatom communities also varied on nanocoated substrata in the presence and the absence of light. The observed AF activity of the ZnO nanocoatings is attributed to the formation of reactive oxygen species (ROS) through photocatalysis in the presence of sunlight. These nanocoatings are a significant step towards the production of an environmentally friendly AF coating that utilizes a sustainable supply of sunlight.

Synthesis of highly permeable Fe2O3/ZnO hollow spheres for printable photocatalysis

We present the deterministic synthesis of mixed-phase Fe₂O₃/ZnO hollow spheres with submicron pores and demonstrate that ink based on these hollow spheres can be used to manufacture stable photocatalytic papers.

Paper-based piezoelectric touch pads with hydrothermally grown zinc oxide nanowires

This paper describes a new type of paper-based piezoelectric touch pad integrating zinc oxide nanowires (ZnO NWs), which can serve as user interfaces in paper-based electronics. The sensing functionality of these touch pads is enabled by the piezoelectric property of ZnO NWs grown on paper using a simple, cost-efficient hydrothermal method. A piece of ZnO-NW paper with two screen-printed silver electrodes forms a touch button, and touch-induced electric charges from the button are converted into a voltage output using a charge amplifier circuit. A touch pad consisting of an array of buttons can be readily integrated into paper-based electronic devices, allowing user input of information for various purposes such as programming, identification checking, and gaming. This novel design features ease of fabrication, low cost, ultrathin structure, and good compatibility with techniques in printed electronics, and further enriches the available technologies of paper-based electronics.

Enhancement in ion adsorption rate and desalination efficiency in a capacitive deionization cell through improved electric field distribution using electrodes composed of activated carbon cloth coated with zinc oxide nanorods

Electrodes composed of activated carbon cloth (ACC) coated with zinc oxide (ZnO) nanorods are compared with plain ACC electrodes, with respect to their desalination efficiency of a 17 mM NaCl solution at different applied potentials. Polarization of the ZnO nanorods increased the penetration depth and strength of the electric field between the electrodes, leading to an increase in the capacitance and charge efficiency at reduced input charge ratios. Uniform distribution of the electric field lines between two electrodes coated with ZnO nanorods led to faster ion adsorption rates, reduced the electrode saturation time, and increased the average desalination efficiency by ∼45% for all applied potentials. The electrodes were characterized for active surface area, capacitance from cyclic voltammetry, theoretical assessment of surface area utilization, and the magnitude of electric field force acting on an ion of unit charge for each potential.

Low-temperature growth of well-aligned zinc oxide nanorod arrays on silicon substrate and their photocatalytic application

Well-aligned and single-crystalline zinc oxide (ZnO) nanorod arrays were grown on silicon (Si) substrate using a wet chemical route for the photodegradation of organic dyes. Structural analysis using X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction confirmed the formation of ZnO nanorods grown preferentially oriented in the (001) direction and with a single phase nature with a wurtzite structure. Field emission scanning electron microscopy and transmission electron microscopy micrographs showed that the length and diameter of the well-aligned rods were about ~350-400 nm and ~80-90 nm, respectively. Raman scattering spectra of ZnO nanorod arrays revealed the characteristic E2 (high) mode that is related to the vibration of oxygen atoms in the wurtzite ZnO. The photodegradation of methylene blue (MB) using ZnO nanorod arrays was performed under ultraviolet light irradiation. The results of photodegradation showed that ZnO nanorod arrays were capable of degrading ~80% of MB within 60 minutes of irradiation, whereas ~92% of degradation was achieved in 120 minutes. Complete degradation of MB was observed after 270 minutes of irradiation time. Owing to enhanced photocatalytic degradation efficiency and low-temperature growth method, prepared ZnO nanorod arrays may open up the possibility for the successful utilization of ZnO nanorod arrays as a future photocatalyst for environmental remediation.

Effect of cationic and anionic surfactants on the application of calcium carbonate nanoparticles in paper coating

Modification of calcium carbonate particles with surfactant significantly improves the properties of the calcium carbonate coating on paper. In this study, unmodified and CTAB (hexadecyltetramethylammonium bromide)- and oleate-modified calcium carbonate nanoparticles were prepared using the wet carbonation technique for paper coating. CTAB (cationic surfactant) and sodium oleate (anionic surfactant) were used to modify the size, morphology, and surface properties of the precipitated nanoparticles. The obtained particles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements, thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM). Coating colors were formulated from the prepared unmodified and modified calcium carbonates and examined by creating a thin coating layer on reference paper. The effect of calcium carbonate particle size and surface modification on paper properties, such as coating thickness, coating weight, surface roughness, air permeability, brightness, whiteness, opacity, and hydrophobicity, were investigated and compared with commercial ground (GCC) calcium carbonate-coated papers. The results show that the obtained calcium carbonate nanoparticles are in the calcite phase. The morphology of the prepared calcium carbonate nanoparticles is rhombohedral, and the average particle diameter is less than 100 nm. Compared to commercial GCC, the use of unmodified and CTAB- and oleate-modified calcium carbonate nanoparticles in paper coating improves the properties of paper. The highest measured paper properties were observed for paper coated with oleate-modifed nanoparticles, where an increase in smoothness (decrease in paper roughness) (+23%), brightness (+1.3%), whiteness (+2.8%), and opacity (+2.3%) and a decrease in air permeability (-26%) was obtained with 25% less coat weight. The water contact angle at a drop age time of 10 min was about 112° for the paper coated with oleate-modified nanoparticles and 42° for paper coated with CTAB-modified nanoparticles compared to 104° for GCC-coated paper.

Antifouling properties of zinc oxide nanorod coatings

In laboratory experiments, the antifouling (AF) properties of zinc oxide (ZnO) nanorod coatings were investigated using the marine bacterium Acinetobacter sp. AZ4C, larvae of the bryozoan Bugula neritina and the microalga Tetraselmis sp. ZnO nanorod coatings were fabricated on microscope glass substrata by a simple hydrothermal technique using two different molar concentrations (5 and 10 mM) of zinc precursors. These coatings were tested for 5 h under artificial sunlight (1060 W m(-2) or 530 W m(-2)) and in the dark (no irradiation). In the presence of light, both the ZnO nanorod coatings significantly reduced the density of Acinetobacter sp. AZ4C and Tetraselmis sp. in comparison to the control (microscope glass substratum without a ZnO coating). High mortality and low settlement of B. neritina larvae was observed on ZnO nanorod coatings subjected to light irradiation. In darkness, neither mortality nor enhanced settlement of larvae was observed. Larvae of B. neritina were not affected by Zn(2+) ions. The AF effect of the ZnO nanorod coatings was thus attributed to the reactive oxygen species (ROS) produced by photocatalysis. It was concluded that ZnO nanorod coatings effectively prevented marine micro and macrofouling in static conditions.

Tuning physical and optical properties of ZnO nanowire arrays grown on cotton fibers

This article reports the first systematic study on the quantitative relationship between the process parameters of solution concentration ratio, structure, and physical and optical properties of ZnO nanowires grown on cotton surfaces. To develop a fundamental understanding concerning the process-structure-activity relations, we grew a series of well-defined, radially oriented, highly dense, and uniform single-crystalline ZnO nanorods and nanoneedles on cotton surfaces by a simple and inexpensive two-step optimized hydrothermal process at a relatively low temperature. This process involves seed treatment of a cotton substrate with ZnO nanocrystals that will serve as the nucleation sites for subsequent anisotropic growth of single crystalline ZnO nanowires. All of the ZnO nanowires exhibit wurtzite crystal structure oriented along the c-axis. For investigating structure-controlled properties, seed-to-growth solutions concentrations ratio ([S]/[G]) of the synthesis process was varied over six different values. Superhydrophobicity was achieved for all morphologies after 1-dodecanethiol modification, which was highly durable after prolonged UV irradiation. Durability of the ZnO materials under laundry condition was also verified. Variation of the [S]/[G] ratio resulted in a morphological transform from nanorods to needle-like structures in conjunction with a drastic change in the physical and optical properties of the ZnO modified cotton surfaces. Higher [S]/[G] ratios yielded formation of ZnO nanoneedles with high degree of crystallinity and higher aspect ratio compared to nanorods. Increasing [S]/[G] ratio resulted in the amount of ZnO grown on the cotton surface to drop significantly, which also caused a decrease in the surface hydrophobicity and UV absorption. In addition, room temperature photoluminescence measurements revealed that the band gap of ZnO widened and the structural defects were reduced as the morphology changed from nanorods to nanoneedles. A similar trend was observed in the UV-vis absorption of nanorods and nanoneedles, the onset of the latter exhibiting a blue-shift that correlates with the widening of band gap with nanoneedle formation.

Zinc oxide-mediated photocatalytic decolorization of Ponceau S in aqueous suspension by visible light

ZnO, comprising nanosize particles (approximately 40 nm) has been prepared by heating (300°C) ZnCO3, which was obtained as precipitate by mixing ZnSO4 and (NH4)2CO3 solutions. The prepared ZnO was characterized by X-ray diffraction, scanning electron microscopy (SEM), laser-induced breakdown spectroscopy, and adsorption studies. It has been used to catalyze the decolorization of Ponceau S (PS), a model diazo dye, in an aqueous suspension under visible light (I ≈ 1.8 × 10−4 W cm−2). This ZnO was found to be more efficient as a photocatalyst compared to pristine ZnO. ZnO samples with higher temperatures (500°C and 700°C) show less catalytic activity. SEM images show that the particle size of ZnO increases with the increase in calcined temperature of ZnO through agglomeration, resulting in a decrease in surface area. Photodecolorization of PS is affected by its and ZnO concentrations, but unaffected by the initial pH of the solutions in the range of 4 to 7. Illumination for a sufficiently long time completely mineralizes the dye, but no Zn2+ can be detected in the clear solution.

Photodegradation kinetics in the ZnO suspension obeys the Langmuir-Hinshelwood equation, and some activation of the ZnO surface by light is indicated.

Paper modified with ZnO nanorods - antimicrobial studies

Paper with antimicrobial properties was developed through in situ growth of ZnO nanorods. The targeted application for this type of paper is in health centers as wallpaper, writing paper, facemasks, tissue paper, etc. The paper was tested on three model microbes, Gram-positive bacteria Staphylococcus aureus, Gram-negative bacteria Escherichia coli and common airborne fungus Aspergillus niger. No viable bacterial colonies or fungal spores could be detected in the areas surrounding test samples of the antimicrobial paper. Gram-negative bacteria Escherichia coli were found to be inhibited in an area that is 239% and 163% the area of the paper sample under different room lighting conditions, i.e., halogen and fluorescent lamp illumination, respectively. For Gram-positive bacteria Staphylococcus aureus the zones of inhibition surrounding the paper samples are 102% and 70%, and for Aspergillus niger, 224% and 183% of the sample area, under similar lighting conditions.