A nanogenerator is a device that utilizes the semiconducting and piezoelectric properties of zinc oxide nanowires. These piezoelectric nanowires are used in the conversion of mechanical energy into electrical energy (Yang et al. pg 1). The nanogenerator produces an electric flow that is continuous from ultrasonic waves. The electric flow that a single nanowire produces can even go up to four watts per centimeter (MLO pg 1).
A nanogenerator benefits from the semiconducting and piezoelectric characteristics of zinc oxide nanostructures which are able to produce micro electric charges when the nanostructures are flexed. The piezoelectric property of zinc oxide transforms the mechanical strain to polarization charges that create a piezoelectric potential. The electrode-nanowire interface has a schottky barrier that directs the electron flow using the piezoelectric potential influence (Yang et al. pg 1).
The design of the nanogenerator was formulated to tap energy from environmental sources which include mechanical vibrations, blood flow and ultrasonic waves. Several approaches aimed at demonstrating nanogenerators have been presented, with the most popular being single wire generator (SWG). This SWG is made up of single zinc nanowires with its ends attached to metal contacts. The zinc nanowires lie on a substrate that is flexible (MLO pg 1).
In the context of this essay zinc oxide is used in nanogenerator which acts as a transducer in the conversion of mechanical energy to electrical energy. Global use of zinc oxide exceeds 1.2 million tons every year. Other uses of zinc oxide include its use in rubber manufacturing to increase the elasticity and strength of rubber. Zinc oxide is also used in concrete manufacturing, anti-corrosive coatings, and cigarette filters.
Pharmaceutical uses of zinc oxide include treatment of irritation and minor burns. Zinc oxide is also of great importance in the manufacture of sunscreen lotion because of its ability to absorb ultraviolet radiation thus eliminating the damages caused by the UV radiation as well as acting as a skin protector from sunburns. According to research conducted to observe exposure related behaviors in humans, it concluded that zinc oxide was not a skin irritant (Occupational Safety & Health Administration para 3).
Human exposure to zinc oxide can occur in various ways, most commonly through inhalation, ingestion, eye or skin contact. Certain operations involve zinc oxide and thus may lead to those conducting the operations to be exposed.
These operations include cosmetics use, use in food additives, photoconductors, seed treatments, photoconductors, and in color photography (United States Department of Labor pg 1). Zinc oxide is believed to affect the reproductive system and the lungs in experimental animals (United States Department of Labor pg 1).
A study to establish the zinc oxide and other sunscreen nanoparticle skin penetration in humans indicated that there was limited penetration, approximately 0.03%, of zinc oxide through the epidermis. Observation by an electron microscope showed that no particles were observed in the stratum corneum indicating that there is limited penetration of nanoparticles through the human skin (Global Nanomaterials Safety pg 13).
Research on the distribution of zinc oxide on the human skin by the utilization of different techniques, that is, multi photon microscopy (MPM) used in a combination with scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) was conducted.
The research indicated that zinc oxide nanoparticles accumulated into skin folds in the stratum corneum. And in some cases it accumulated as hair follicle roots. Considering the poor penetration zinc oxides have through the startum corneum, it suggests that zinc oxide penetration through the skin is not likely to cause any health concerns (Global Nanomaterials Safety pg 13).
A study on the possible acute toxicity of zinc oxide was conducted using adult healthy mice as a specimen. The study showed that there is little variation in the toxic effects of 20nm and 120nm of zinc oxide. There are indications that a relationship exists between the size of the zinc oxide particles and the effect. The research however concluded that the particles of zinc oxide are not toxic. Acute zinc oxide exposure is believed to cause respiratory irritation, nausea, fever, vomiting, chills and coughing (United States Department of Labor pg 1).
Analysis on the possible effects of repeated dose toxicity of zinc oxide through inhalation was conducted in animals. When rats inhaled zinc oxide for five days, local lung inflammations were observed. These lung inflammations were observed by alterations in certain parameters in histological examinations and the bronchoalveolar levage fluid (BALF).
Apart from this inflammation, draining of the lymph nodes was also observed. The effects were reversible in a certain recovery period and they were related to the concentration inhaled. Chronic zinc oxide exposure through the skin is believed to cause skin “papular-pustullar skin eruptions” in the pubic regions, scrotum, and inner thigh and in the inner arm (United States Department of Labor pg 1).
The effects of zinc oxide exposure on the cell morphology were drastic within the first 24hours of exposure. This was more pronounced when the concentrations inhaled were higher than 50micrograms per milliliter. This was witnessed by the cell shrinking and attaining an irregular shape. At higher concentrations of about 100micrograms per milliliter, the cells become detached and necrotic. However, concentrations less than 10micrograms per milliliter caused no observable change on the cells (Wan-Seob pg 4).
When exposed to approximately 50-100 micrograms per milliliter of zinc oxide, an estimated 15-50% of the cells died as indicated using the trypan blue dye technique. Concentrations less than 25micrograms per milliliter of zinc oxide did not cause any significant effect on the cell viability. The permissible exposure limit as set by the Occupational Safety and Health Administration is 15milligrams per cubic meter for zinc oxide (United States Department of Labor pg 1).
A 24 hour exposure of 100micrograms per milliliter lowered the functioning of the mitochondrion by over 80%. These results indicated also that the toxicity of zinc oxide was much higher relative to nanoparticles from other metal oxides. Measures that are aimed at controlling zinc oxide exposures include; exhaust ventilation, wearing protective equipments, process enclosure and general dilution ventilation among others (United States Department of Labor pg 1).
Exposure to inhaled zinc oxide is determined by using a polyvinyl chloride filter followed respirable fraction sampling using a 10mm nylon cyclone. Collection of sample is done at a flow rate of 1.7liters per minute (respirable fraction) on the upper limit until a collection of 816 liters on the upper side is achieved.
For sample collection on total dust, collection is conducted at a flow rate of 2.0 liters per minute on the upper side; collection is continued until a total of 960 liters is achieved. Gravimetric techniques are used in the analysis procedure (United States Department of Labor pg 1).
Absence of epidemiological data is catered by research results obtained from animal studies. Risk management strategies to reduce exposure time and concentration include emergency planning requirements. Hazardous wastes should meet reportable quantity requirements. The employers should give annual submissions of the quantities of zinc oxide releases in their facility as an attempt at informing the community.
The workers should take it as their responsibility to observe respiratory protection policy which includes the conditions for the use of a respirator and the guidelines of the protection program. Selection of clothing and equipments to be used for personal protection by the workers should be conducted carefully. Frequent evaluation of protective clothing should be conducted to establish the effectiveness of these clothing in stopping dermal contact.
Ultrafine particles are very small, about 100 nanometers, and they result from activities such as cleaning, cooking, operation of consumer appliances and smoking tobacco products among other activities. Health risks occur as a result of ultrafine particles.
The small particles pose more risk because they display a greater proportion of their atoms since their surface area is large. Ultrafine particles can either be characterized as natural or anthropogenic. Natural sources of UFP’s include forest fires, forest fires, viruses, biogenic magnetite among others.
Anthropogenic sources which are human generated sources can be categorized as intentional and unintentional. Nanoparticles fall under the intentional anthropogenic sources while unintentional anthropogenic sources comprise jet engines, frying, grilling, metal fumes, and incinerators among others. Excessive exposure to UFPs can cause oxidative inflammation of the lungs and as a result can act as a tool in catching infections like pneumonia, asthma, chronic bronchitis among others (Air Quality Sciences pg 1).
Air Quality Sciences. Ultrafine particles why all the concern about something so small? n.d. Web. 01 Dec. 2011 http://www.aerias.org/uploads/Ultrafine_Particles_FINAL.pdf>
Global Nanomaterials Safety. Toxiological review of nano zinc oxide. PROSPECT: Global Nanomaterials Safety. 8 September, 2009. Web. 1 Dec. 2011 http://www.nanotechia-prospect.org/managed_assets/files/prospect_nano-zno_literature_review.pdf
MLO (Medical Laboratory Observer). “New technology.” MLO: Medical Laboratory Observer 39.7 (2007): 68-68.
Occupational Safety & Health Administration (OCHA). Occupational safety and health guideline for zinc oxide. United States Department of Labour, n. d. Web. 01 Dec. 2011 http://www.osha.gov/SLTC/healthguidelines/zincoxide/recognition.html
Wan-Seob, Cho et al. “Metal oxide nanoparticles induce unique inflammatory footprints in the lung: important implications for nanoparticle testing.” Environmental Health Perspectives 118.12 (2010): 1699-1706.
Yang, Rusen, Qin Yong, Li Cheng, Dai Liming and Wang Zhong Lin. “Characteristics of output voltage and current of integrated nanogenerators.” Applied Physics Letters 94.2