packaging systems can be categorized as scavengers, blockers, releasers, and regulators [84]. The focus here is to protect the food products from harmful microbes [90], excess moisture [91], and excess oxygen [92]. Active antimicrobial packaging systems are combinations of antimicrobial agents and nanomaterials. For example, antimicrobial nanofibrous films of polyvinyl alcohol‐b‐cyclodextrin with cinnamon essential oil performed well in suppressing the growth of Staphylococcus aureus and Escherichia coli [93]. Substitution of cinnamon essential oil with lemongrass and oregano essential oils exhibited suppression of Salmonella enteritidis in ground beef placed in a sterile plastic bag for six days [94]. For reduction of the rate of oxygen transmission, ascorbic and iron powders or copper chloride can be used as catalysts for oxygen scavenging thermoplastic starch films. This method reduces the oxygen transmission rate from 20.9% to 1% in 15 days at 80% relative humidity (RH) [93]. Additionally, for the modification of atmosphere packaging, oxygen scavenging polyethylene terephthalate (PET) films, PET‐aluminum oxide coatings, polylactic acid films, and oriented polypropylene (o‐PP) films were deposited with palladium layers through vacuum deposition on the silicon oxide layer. This method was also able to significantly reduce the oxygen transmission rate [91]. Similarly, low‐density polyethylene (LDPE) films combine with activated carbon and sodium erythorbate exhibited the oxygen concentration absorbance rate of 80% [92].
1.4 Human Health and the Environment
Presently, environmental sustainability is recognized as one of the biggest issues fueled by and affecting humankind. Directly related to the continuous increase in population, the constant deteriorating environmental health is holding us back from achieving global sustainability. Moreover, almost every aspect of sustainability discussed in this chapter either is dependent upon the environment or contributes to its condition [95]. Although there are many aspects of the environment that can be improved to prevent any more damage, the three discussed here are air, water, and energy. The influence of nanotechnology can enhance these three facets of the environment in a safe manner and minimize the effects of any future anthropogenic activities.
1.4.1 Water Purification
Clean water is an essential part of global sustainability. The constantly increasing the global human population increases the demand for clean water; however, population increase is also a factor in the growth of industries, a huge factor in the decrease in water quality. Making clean and affordable water accessible to people is still a challenge today [96]. There are various conventional methods used today for water treatment and purification. Nanomaterial‐based water purification methods, however, not only improve the quality of water but also extend purification treatments to remote areas without electricity [97]. Many nanomaterials used in nano oncology and for drug delivery are also utilized in water treatments. For example, CNTs, in this case acting as nano adsorbents, are better alternatives of activated carbon because they are able to absorb organic chemicals more efficiently than activated carbon [98].
Nanomembranes are another method of removing microparticles from water. These membranes are composed of nanofibers and, when combined with metal oxide nanoparticles, can intensify membrane surface hydrophilicity, water permeability, and fouling resistance [96]. Nanocatalysts, such as zero‐valent metal, semiconductor materials, and bimetallic nanoparticles, are used in purification treatment to amplify reactivity and degradation of contaminants such as pesticides and herbicides [99]. Studies show that silver nanocatalysts, N‐doped TiO₂, and ZrO₂ nanoparticles are successful in the degradation of contaminants in water [100]. Similar to nanocatalysts, nanostructured catalytic membranes also have higher rates of decomposition and selectivity. These membranes require less contact time, can be scaled for commercial purposes, are composed of homogeneous catalytic sites, and allow multiple reactions to take place simultaneously [101].
1.4.2 Air Purification
Air is a unique essential resource needed by living beings. Unlike water, living without air is quite impossible for aerobic species. With water, part of the problem is that it is inaccessible to some remote areas of the world. With air the situation is different because there is an abundance of breathable air, the only problem is the quality of it. As the global population increases and continues to spread, the result is the settlement of factories and other industrial buildings and an increase in automobile use, which contributes to the poor quality of breathable air.
Some examples of nanotechnology used in air purification methods are CNTs, GNPs, and nanocatalysts. CNTs have a small pore structure and large surface area of functional groups, which can be manipulated through optimum chemical or thermal treatment. These characteristics allow CNTs to be highly efficient in trapping perilous substances from the air [102]. Unlike CNTs, GNPs have shown to exhibit converting characteristics. For example, when combined with titanium dioxide, GNPs are able to convert sulfur dioxide present in polluted air into sulfur [103]. Nanocatalysts also exhibit converting characteristics. The surface area of these catalysts is large enough for chemical reactions to take place. These reactions are able to convert the harmful gases produced by automobiles and factories into safe gases.
1.4.3 Energy
Water and air are essential to the survival of most living beings, but for humans, energy has become as important. As much as we promote the use of alternative sources for energy, most of it is still produced from fossil fuels. This has a huge impact on the environment and is actually a barrier to achieving sustainability. Fossil fuels may have been an excellent source for many of our needs, but it certainly has proved to not be a reliable source. First, fossil fuels are considered to be nonrenewable resources, i.e. at one point we would have to deal with their depletion and find reliable alternative resources for our needs. Additionally, this resource is not readily available to everyone because of its uneven distribution – a huge concern for those who are not able to access it [104, 105]. There are many alternative sources of energy available, most popular being solar energy, but they have not been used at a large scale due to issues with converting nonrenewable sources to renewable energy and minimizing energy loss [106]. The use of nanotechnology in the energy sector is able to provide clean energy in a cost‐effective way by developing both conventional and renewable energy sources.
1.4.3.1 Energy Conversion
Even though there are many forms of energy available to us, we cannot directly use them. In everyday life, the most useful forms of energy for us are electrical and heat energy, but they can only be generated through conversion from other forms of energy. In reality, all forms of energy, including nuclear energy, come from the sun, hence solar energy is the common source. This energy can be converted to chemical, heat, wind/hydro, and mechanical energy, all of which can be ultimately converted to electrical energy, the most common form of energy used [107]. Every day, the sun releases a huge amount of energy, making solar energy abundant and cost‐free. This energy is released in the form of heat and radiation. Using photovoltaic cells, sunlight can be converted into solar energy that can then be converted into other forms of energies [108]. Conventional solar cells have two drawbacks; they are expensive to produce and their efficiency is rarely above 20%. This is mainly due to the energy of the photons in the cell being larger than the bandgap energy, the right amount of energy needed for the solar cell to work. To correct this, solar cells are enhanced with quantum dots. Due to their variation in size, quantum dots are able to produce various bandgaps that allow the photons that previously had larger energy to pass through. In addition, solar cells made of nanomaterials, such as nanocrystalline silicon, are capable of increasing the efficiency of solar cells by 40–50% [109].
1.4.3.2 Energy Production
Some of the already discussed nanomaterials can be used to make already established energy production mechanisms more effective. To make solar cells more cost‐efficient and effective, organic materials
