Smart materials and Green Synthesis: The perfect match for the future

Materials science seeks the development of new materials with optimized characteristics. The union of various areas as chemistry, physics, nanotechnology, biology, and medicine catalyzes news materials. Smart materials react to external stimuli by modifying their chemical, mechanical, magnetic, optical, electrical, thermal properties. They have superior efficiency to the materials currently available and promise many advantages to their consumers. However, smart materials must be associated with sustainable technological progress. As a result of highly evolved technologies and intense laboratory research, their final characteristics must be connected with sustainable protocols. In addition to a significant difference associated with a wide application in various areas as textile industry, construction, medicine, drugs delivery, microorganisms’ detection, smart materials must not pollute from production to disposal, and more than that, they must seek compensation for the harmful effects of this evolution on nature. In this way, smart materials will be an excellent advantage for the future and the environment.


Introduction
Materials science connects the areas of chemistry, physics, nanotechnology, biotechnology, and engineering. The search for understanding the functionality of existing materials and their physical, chemical, and biological properties catalyzes the development of new materials that have optimized functions, with eco-friendly syntheses and excellent efficiency. Thus, new products are established for new consumers [1].
Smart materials arise with the new vision of the connection between various experts to develop responsive materials, which are materials that dynamically respond to external stimuli. These materials represent a great innovation for different areas such as textile industries [2], constructions [3], development of materials for drug delivery [4], among others.
Countless studies in the recent literature seek new technologies associated with smart materials. Materials with shape memory, for example, can return to their original shape, even after having undergone external stimuli, such as thermal expansion and tension [5]. The chromoactive materials are being used a lot in optical sensors because they promote color changes after an external stimulus, such as temperature, pH, pressure, allowing the detection of pollutants in water [6]. Nanosensors have broad applications in biology, detecting contaminated water, medicine through detecting malignant tumors and detecting microorganisms. These sensors have low-cost, fast synthesis routes and are highly sensitive and efficient [7]. Piezoelectric materials, such as piezoelectric ceramics, can convert electrical energy into mechanics and vice versa [8]. Magnetorheological materials modify their properties with magnetic fields, thus preventing vibrations in bridges and large buildings [9].
Observations of natural phenomena help in predicting new materials. The synthetic spider web is one of them. Its resistance, around five times greater than steel, still enables elasticity. Thus, the development of armor or bulletproof vests can be replaced by bulletproof clothing and fibers for surgical sutures with high resistance and lightly strained cables and cables but excellent resistance to traction [10].
Graphite, graphene, and reduced graphene oxide (rGO) and their multiple properties have several applications. Also, they can be associated with other materials, such as plastics, generating batteries with high autonomy and flexibility [11]; hybrids of graphene and metal oxides that produce efficient solar cells [

Green synthesis of Smart Materials
Green chemistry sets out principles that establish criteria that must be followed in order for the final product to have a beneficial connection with the environment [17]. 10. Design of chemicals and products to degrade after use.
11. Analysis in real-time to avoid pollution.

Minimize the potential for accidents
Based on these concepts and seeking to combine them with the development of smart materials, it is essential to establish that smart materials should have better features associated with what they were intended for and have their origin in green syntheses to respect these principles-previously mentioned, protecting the environment and humanity. Thus, the planet will integrally benefit from smart materials. Thus, the search for smart materials based on green synthesis is increasingly urgent so that the impact of consumerism does not generate damage to the environment.
The green synthesis of magnetite nanoparticles (Fe3O4) using Chromolaena odorata root extract to produce an intelligent nanocomposite represents an advantage. In addition to being environmentally friendly, they are also responsible for stimuli [18]. The Green Synthesis of Zeolite / Fe2O3 Nanocomposites can act as an intelligent and non-toxic nanofertant following the precepts of green chemistry [19]. The antimicrobial efficiency for combating bacteria resistant to antibiotics and eradicating bacterial biofilms in a hospital environment was obtained by green synthesis from the essential oil of Eucalyptus globulus to produce zinc oxide nanoparticles [20]. Intelligent fabrics obtained through treatment with silver nanoparticles obtained by green synthesis are also widely studied. This is because protection against the proliferation of microorganisms in hospital environments is of paramount importance. The green synthesis of silver nanoparticles from Plinia Cauliflora extract showed efficiency, avoiding this proliferation [21]. A nanothermometer and chromium IV ion sensor was obtained by eco-friendly synthesis and has a wide temperature range from 5 to 65∘C and high efficiency for detecting hexavalent chromium ions in water samples [22]. A biosensor based on a biopolymer and silver nanoparticles, synthesized by the green route, is an optical ammonia sensor for clinical diagnosis detection of ammonia level in biological fluids for several in humans [23]. And not only for ammonia, but the green route produces many biosensors to detect hydrogen peroxide, pollutants in the environment, microorganisms, gas sensors, and even malignant tumors [24][25][26][27][28][29]. Green synthesis of carbon-graphene nanotube hybrids demonstrated efficiency in water purification [30]. There is also the chemical modification with biodegradable molecules for the graphene hydrogel for gas detection [31]. For supercapacitors' flexible electronic applications, the green synthesis of autonomous cellulose/graphene oxide/polyaniline aerogel electrode is possible [32].
Given so many examples, it appears that the development of smart materials based in green chemistry, it is possible and desirable to apply these smart materials to connect their potential with the environment (Figure 1).

Conclusion
The revolution that smart materials can cause soon is incredible, and it is still challenging to predict the real impact of these new technologies on world society. However, humanity needs to understand that new materials must be based on eco-friendly products, from their synthesis, useful life, and disposal. The search for new materials must accompany the search of the world population. There is no point in having new materials, called smart, if humanity is not careful from its prospecting, synthesis, the study of useful life, and environmental impact. The scientific community must seek solutions for existing products, making them dynamic, efficient, and responsible for the environment, as the opposite will result in more consumerism and impact on nature. Smart materials should focus on implementing efficient technologies with environmental respect. Only then, not only will the materials be considered intelligent, but producers and consumers as well.