Hybrid nickel-free graphene/porphyrin rings for photodegradation of emerging pollutants in water

Probing mechanism of Rhodamine B decolorization under homogeneous conditions via pH-controlled photocatalysis with anionic porphyrin

Porphyrins are acknowledged for their efficacy as photosensitizers and show potential for the treatment of water contaminated with diverse dyes. This research emphasizes the use of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) as a photosensitizer for purifying water contaminated with rhodamine B. Investigations were conducted under homogeneous conditions using visible light irradiation, revealing the efficacy of the porphyrin in the decolorization of rhodamine B strongly depends on pH of the solution. This study demonstrated that within 120 min, the decolorization process rapidly removed about 95% of RhB at an initial pH of 3.0, while at pH 6.0, the removal rate was significantly lower, at only 12%. An extensive photophysical study of the TPPS was carried out at pH 6.0 and pH 3.0 including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, triplet and singlet oxygen quantum yields in order to explain difference in the efficiency of RhB discoloration. A thorough investigation into mechanism revealed that neither reactive oxygen species nor singlet oxygen played a role in RhB decolorization within this system. Instead, the predominant route was found to be the electron transfer from photoexcited TPPS to RhB, followed by proton transfer at pH 3.0, leading to the generation of a colorless leuco form.

Band Engineering versus Catalysis: Enhancing the Self-Propulsion of Light-Powered MXene-Derived Metal-TiO2 Micromotors To Degrade Polymer Chains

Light-powered micro- and nanomotors based on photocatalytic semiconductors convert light into mechanical energy, allowing self-propulsion and various functions. Despite recent progress, the ongoing quest to enhance their speed remains crucial, as it holds the potential for further accelerating mass transfer-limited chemical reactions and physical processes. This study focuses on multilayered MXene-derived metal-TiO2 micromotors with different metal materials to investigate the impact of electronic properties of the metal-semiconductor junction, such as energy band bending and built-in electric field, on self-propulsion. By asymmetrically depositing Au or Ag layers on thermally annealed Ti3C2Tx MXene microparticles using sputtering, Janus structures are formed with Schottky junctions at the metal-semiconductor interface. Under UV light irradiation, Au-TiO2 micromotors show higher self-propulsion velocities due to the stronger built-in electric field, enabling efficient photogenerated charge carrier separation within the semiconductor and higher hole accumulation beneath the Au layer. On the contrary, in 0.1 wt % H2O2, Ag-TiO2 micromotors reach higher velocities both in the presence and absence of UV light irradiation, owing to the superior catalytic properties of Ag in H2O2 decomposition. Due to the widespread use of plastics and polymers, and the consequent occurrence of nano/microplastics and polymeric waste in water, Au-TiO2 micromotors were applied in water remediation to break down polyethylene glycol (PEG) chains, which were used as a model for polymeric pollutants in water. These findings reveal the interplay between electronic properties and catalytic activity in metal-semiconductor junctions, offering insights into the future design of powerful light-driven micro- and nanomotors with promising implications for water treatment and photocatalysis applications.

Light-Propelled Nanorobots for Facial Titanium Implants Biofilms Removal

Titanium miniplates are biocompatible materials used in modern oral and maxillofacial surgery to treat facial bone fractures. However, plate removal is often required due to implant complications. Among them, a biofilm formation on an infected miniplate is associated with severe inflammation, which frequently results in implant failure. In light of this, new strategies to control or treat oral bacterial biofilm are of high interest. Herein, the authors exploit the ability of nanorobots against multispecies bacterial biofilm grown onto facial commercial titanium miniplate implants to simulate pathogenic conditions of the oral microenvironment. The strategy is based on the use of light-driven self-propelled tubular black-TiO₂ /Ag nanorobots, that unlike traditional ones, exhibit an extended absorption and motion actuation from UV to the visible-light range. The motion analysis is performed separately over UV, blue, and green light irradiation and shows different motion behaviors, including a fast rotational motion that decreases with increasing wavelengths. The biomass reduction is monitored by evaluating LIVE/DEAD fluorescent and digital microscope images of bacterial biofilm treated with the nanorobots under motion/no-motion conditions. The current study and the obtained results can bring significant improvements for effective therapy of infected metallic miniplates by biofilm.

Shape-Controlled Self-Assembly of Light-Powered Microrobots into Ordered Microchains for Cells Transport and Water Remediation

Nature presents the collective behavior of living organisms aiming to accomplish complex tasks, inspiring the development of cooperative micro/nanorobots. Herein, the spontaneous assembly of hematite-based microrobots with different shapes is presented. Autonomous motile light-driven hematite/Pt microrobots with cubic and walnut-like shapes are prepared by hydrothermal synthesis, followed by the deposition of a Pt layer to design Janus structures. Both microrobots show a fuel-free motion ability under light irradiation. Because of the asymmetric orientation of the magnetic dipole moment in the crystal, cubic hematite/Pt microrobots can self-assemble into ordered microchains, contrary to the random aggregation observed for walnut-like microrobots. The microchains exhibit different synchronized motions under light irradiation depending on the mutual orientation of the individual microrobots during the assembly, which allows them to accomplish multiple tasks, including capturing, picking up, and transporting microscale objects, such as yeast cells and suspended matter in water extracted from personal care products, as well as degrading polymeric materials. Such light-powered self-assembled microchains demonstrate an innovative cooperative behavior for small-scale multitasking artificial robotic systems, holding great potential toward cargo capture, transport, and delivery, and wastewater remediation.

Lerf-Klinowski-type models of graphene oxide and reduced graphene oxide are robust in analyzing non-covalent functionalization with porphyrins

Graphene-based nanohybrids are good candidates for various applications. However, graphene exhibits some unwanted features such as low solubility in an aqueous solution or tendency to aggregate, limiting its potential applications. On the contrary, its derivatives, such as graphene oxide (GO) and reduced graphene oxide (RGO), have excellent properties and can be easily produced in large quantities. GO/RGO nanohybrids with porphyrins were shown to possess great potential in the field of photocatalytic hydrogen production, pollutant photodegradation, optical sensing, or drug delivery. Despite the rapid progress in experimental research on the porphyrin-graphene hybrids some fundamental questions about the structures and the interaction between components in these systems still remain open. In this work, we combine detailed experimental and theoretical studies to investigate the nature of the interaction between the GO/RGO and two metal-free porphyrins 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) and 5,10,15,20-tetrakis(4-hydroxyphenyl) porphyrin (TPPH)]. The two porphyrins form stable nanohybrids with GO/RGO support, although both porphyrins exhibited a slightly higher affinity to RGO. We validated finite, Lerf-Klinowski-type (Lerf et al. in J Phys Chem B 102:4477, 1998) structural models of GO ([Formula: see text]) and RGO ([Formula: see text]) and successfully used them in ab initio absorption spectra simulations to track back the origin of experimentally observed spectral features. We also investigated the nature of low-lying excited states with high-level wavefunction-based methods and shown that states' density becomes denser upon nanohybrid formation. The studied nanohybrids are non-emissive, and our study suggests that this is due to excited states that gain significant charge-transfer character. The presented efficient simulation protocol may ease the properties screening of new GO/RGO-nanohybrids.

Innovative Polymeric Hybrid Nanocomposites for Application in Photocatalysis

The immobilization of inorganic nanomaterials on polymeric substrates has been drawing a lot of attention in recent years owing to the extraordinary properties of the as-obtained materials. The hybrid materials, indeed, combine the benefits of the plastic matter such as flexibility, low-cost, mechanical stability and high durability, with them deriving from their inorganic counterparts. In particular, if the inorganic fillers are nanostructured photocatalysts, the originated hybrid systems will be able to utilize the energy delivered by light, catalysing chemical reactions in a sustainable pathway. Most importantly, since the nanofillers can be ad-hoc anchored to the macromolecular structure, their release in the environment will be prevented, thus overcoming one of the main restrictions that impedes their applications on a large scale. In this review, several typologies of hybrid photocatalytic nanomaterials, obtained by using both organic and inorganic semiconductors and realized with different synthetic protocols, were reported and discussed. In the first part of the manuscript, nanocomposites realized by simply blending the TiO2 or ZnO nanomaterials in thermoplastic polymeric matrices are illustrated. Subsequently, the atomic layer deposition (ALD) technique is presented as an excellent method to formulate polymeric nanocomposites. Successively, some examples of polyporphyrins hybrid systems containing graphene, acting as photocatalysts under visible light irradiation, are discussed. Lastly, photocatalytic polymeric nanosponges, with extraordinary adsorption properties, are shown. All the described materials were deeply characterized and their photocatalytic abilities were evaluated by the degradation of several organic water pollutants such as dyes, phenol, pesticides, drugs, and personal care products. The antibacterial performance was also evaluated for selected systems. The relevance of the obtained results is widely overviewed, opening the route for the application of such multifunctional photocatalytic hybrid materials in wastewater remediation.

A π-π stacking perylene imide/Bi2WO6 hybrid with dual transfer approach for enhanced photocatalytic degradation

A new broad-spectrum responsive organic-inorganic hybrid photocatalyst (PI@BWO) was successfully prepared by in-situ growing Bi₂WO₆ nanosheets onto the surface of π-π stacking perylene imide. The obtained PI@BWO hybrids with different composition exhibited enhanced photocatalytic activity for Bisphenol A (BPA) degradation. Among them, 30% PI@BWO exhibited optimal photocatalytic degradation efficiency, which is 2.6 and 3.9 times higher than that of pristine PI and BWO, respectively. Furthermore, PI@BWO also performed good stability and recyclability. Remarkably, the π-conjugation of PI facilitated the separation of charge carriers and improved the utilization of sunlight for PI@BWO. The introduction of BWO nanosheets also enhanced the adsorption capacity for contaminants and provided much more plentiful active sites, promoting the next photocatalytic reaction. Most importantly, PI@BWO could produce abundant reactive species (such as ¹O₂ and ·OH) via the charge carrier transfer and energy transfer dual transfer approach, therefore leading to stronger oxidation ability. The photocatalytic degradation mechanism and pathway of the PI@BWO hybrids were finally proposed. Overall, this present work might provide a new insight into the designing and preparation of efficient organic-inorganic hybrid photocatalysts for environmental-friendly removal of hazardous organic pollutants.

Graphene Oxide Functionalized with Cationic Porphyrins as Materials for the Photodegradation of Rhodamine B

Two noncovalent nanohybrids between cationic porphyrin (free-base TMPyP and zinc(II) ZnTMPyP) bearing cationic (N-methylpyridyl) groups and graphene oxide (GO) were constructed with the aim of generating a photocatalyst active for rhodamine B (RhB) degradation. The obtained materials were thoroughly characterized by steady-state and time-resolved absorption and emission methods, which indicated that metalation of the porphyrin with Zn(II) increases the affinity of the porphyrin toward the GO surface. Photocurrent experiment together with femtosecond transient absorption spectroscopy clearly showed the existence of electron transfer from the photoexcited porphyrin to GO. Both hybrid materials demonstrated higher photocatalytic activity toward RhB degradation as compared to GO; however, ZnTMPyP-GO exhibited more efficient performance (19% of RhB decomposition after 2 h of irradiation). Our data indicate that the presence of Zn(II) in the core of the porphyrin can promote charge separation in the ZnTMPyP-GO composites. The higher degradation rate seen with ZnTMPyP-GO as compared to the TMPyP-GO assemblies highlights the beneficial role of Zn(II)-metalation of the porphyrin ring.