Periodic Reporting for period 1 - STIMULATOR (Sunlight Active Mesoporous Black TiO2 Micro/Nanomotors)
Período documentado: 2021-10-01 hasta 2023-09-30
Microplastics can reach the human body by inhalation and ingestion causing inflammation or cell damage. Recently microplastics have been found in the human bloodstream and stool. Most of the microplastics were polystyrene (from food packaging), polyethylene terephthalate (from drinking bottles), and polyethylene (from carrier bags). Hence increased reliance on plastic can cause their absorption by organs, and even cells, which can lead to carcinogenicity, chronic toxicity, genotoxicity, and developmental toxicity. Water-soluble polymers such as polyvinyl alcohol (a polymer used in textiles, paper industries, and in households as detergent pods) and polyethylene glycol (a main ingredient in cosmetics) are also of similar concern. The European Union (EU) circular economy action plan targets microplastics by highlighting the need to tackle the unintentional release of microplastics into the aquatic environment. If not removed during wastewater treatment, these microplastics could enter the aquatic ecosystem in estimated quantities of several thousand tons annually and, hence, to the body of living organisms. Hence, there is a pressing need for an eco-friendly, highly economical, and efficient strategy for the degradation of microplastics. Unlike conventional polymer degradation techniques, light-powered robots can address this problem in a sustainable way. This project, STIMULATOR has developed a longer wavelength (NIR) absorbing single component H2Ti3O7 microrobots from a UV-absorbing white TiO2 mesostructured microrobots for the phototrapping and photofragmentation of microplastics such as polystyrene (PS), polyethylene glycol (PEG) and polyvinyl alcohol (PVA) for the first time. Using external light sources limits the commercial success of micro/nanorobots (MNRs) which cannot propel under NIR in their single-component form. Hence, it is highly demanding to fabricate a material with UV, Visible, and NIR absorption (natural sunlight utilization) features with no post-synthetic treatment that could lead to a new class of MNRs in the scientific world that could be used and propelled under direct sunlight for the first time for water treatment. These MNRs once achieved, can not only work as a photocatalytic robot for water purification but also in biomedical applications such as anticancer therapy, drug delivery, etc. STIMULATOR addressed these problems and generated new knowledge on robotic research and offer a path for the sustainable degradation of microplastics, mitigating the poisoning of aquatic ecosystems due to microplastics. As the EU is specifically looking for the development and modernization of wastewater treatment plants as part of SDGs, the results of STIMULATOR will be impactful and extremely important owing to the establishment of cutting-edge technology that can support the EU sustainable developmental goals.
Hence, the overall objectives of STIMULATOR were 1) Synthesis of mesoporous TiO2 structures (MT); 2) Tuning MT to MT robots (MTRs); 3) MTRs to Mesoporous black TiO2 based robots (MBTRs); 4) Implementation of MBTRs in microplastics trapping and degradation.
Hence, the overall objectives of STIMULATOR were 1) Synthesis of mesoporous TiO2 structures (MT); 2) Tuning MT to MT robots (MTRs); 3) MTRs to Mesoporous black TiO2 based robots (MBTRs); 4) Implementation of MBTRs in microplastics trapping and degradation.
A single-component rod-like TiO2 superstructures with self-propulsion ability has been developed. These autonomous superstructured microrobots possessed expansion-contraction of microrobot school mechanism under UV light on-off procedure. They have shown the capability of in situ surface morphing to convert the surface with mesostructured nanoseed array into flower-like architectures. These flower-like architectures on the surface facilitated photocatalytic trapping of polystyrene into the vacant spaces available between the curly constructions present. Furthermore, we have demonstrated the photodegradation of high molecular weight polyethylene glycol. The characterization using MALDI-MS confirmed that the polymer was photodegraded into its lower mass compounds. Hence this work illuminates the understanding of synthesizing single-component asymmetric superstructure microrobots of TiO2 for phototrapping and photodegradation of microplastics and other suspended pollutants in water.
Due to the success of this material, this work has been extended to form the black titanates for absorbing not only UV and visible but also the NIR (700 – 2500 nm) region of the solar spectrum. The formation of black TiO2 was expected by the chemical reduction of TiO2 MNRs under an inert atmosphere. However, the structure formed was black H2Ti3O7, and it was asymmetric in structure. Interestingly, diverse motion behaviour was observed under different light sources such as A) UV (λ = 365 nm), B) Blue (λ = 455 nm), and C) continuous halogen light (λ = 350 – 2500 nm) light. Under UV, the motion was expansion-schooling like what was observed in the parent TiO2 MNRs, whereas when the blue light source was used, both expansion-schooling and collective motion were observed. Interestingly, by using the halogen lamp (350 – 2500 nm), only collective motion was observed without an expansion-schooling mechanism.
Due to the success of this material, this work has been extended to form the black titanates for absorbing not only UV and visible but also the NIR (700 – 2500 nm) region of the solar spectrum. The formation of black TiO2 was expected by the chemical reduction of TiO2 MNRs under an inert atmosphere. However, the structure formed was black H2Ti3O7, and it was asymmetric in structure. Interestingly, diverse motion behaviour was observed under different light sources such as A) UV (λ = 365 nm), B) Blue (λ = 455 nm), and C) continuous halogen light (λ = 350 – 2500 nm) light. Under UV, the motion was expansion-schooling like what was observed in the parent TiO2 MNRs, whereas when the blue light source was used, both expansion-schooling and collective motion were observed. Interestingly, by using the halogen lamp (350 – 2500 nm), only collective motion was observed without an expansion-schooling mechanism.
STIMULATOR has developed mainly two single-component mesoporous microrobots. 1) In situ surface morphed TiO2 microrobots and 2) black H2Ti3O7 microrobots with NIR absorption for the first time. Unlike the objectives set in the proposal, the work has gone far beyond the state of the art that no harsh chemical or post synthetic treatment such as sputtering and ALD were used as part of STIMULATOR. It is also worth mentioning that two complex EU sustainable development goals such as 1) water quality and sanitation and 2) good health, and well-being are addressed here by carrying out microplastics trapping and fragmentation. One of the MNRs synthesized as part of STIMULATOR, H2Ti3O7 has shown NIR absorption and symmetric morphology led towards self-propulsion under a halogen lamp (350 – 2500 nm) mimicking natural sunlight. This will pave the way for the large-scale production of single component MNRs and their application in direct sunlight active photocatalysis. The first microrobot shows the capability of TiO2 for in situ surface morphing during the phototrapping of polystyrene microplastics and paved the way for the formation of flower-like curly architectures to trap polystyrene beads. The second exciting material, H2Ti3O7 has shown NIR absorption and was self-propelled under a wide spectrum light source of 350 – 2500 nm wavelength, showing its ability to harvest direct sunlight. This work enlightens the pathway towards the applicability of MNRs in direct sunlight-powered photocatalysis for the degradation of microplastics, which are considered one of the major threats to living organisms. These MNRs can be extended to photothermal and photodynamic therapy. The single-component nature and easy synthetic methods pave the way for their large-scale fabrication. Hence the utilization of longer wavelength (≤ 2500 nm) controlled MNRs and their microplastic degradation has high impact to the society.