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Advanced oxidation processes stand as green alternatives for the decontamination of waste waters. Photocatalysis is an advanced oxidation process in which a semiconductor material absorbs photon energy and triggers redox reactions capable of degrading organic pollutants. Titanium dioxide (TiO 2 , titania) represents one of the most popular choices of photocatalytic materials, however the UV-activation of its anatase phase and its high charge recombination rate decrease its photocatalytic activity and weaken its potential. Graphene oxide is a 2D carbon nanomaterial consisting of exfoliated sheets of hexagonally arranged carbons decorated with oxygen- and hydrogen- functional groups. Composite nanomaterials consisting of titania nanoparticles and graphene oxide have proven to enhance the photocatalytic activity of pure TiO 2 . In this review, we present a thorough literature review of ternary nanocomposites based on synthesized or commercial titania nanoparticles and GO (or reduced GO) particularly used for the photodegradation of dyes. GO/TiO 2 has been enriched primarily with metals, semiconductors and magnetic nanomaterials, proving a superior dye degradation performance and reusability compared to bare TiO 2 . Ongoing challenges and perspectives are outlined.

Mesostructured PbO 2 /TiO 2 materials were synthesized to perform electrocatalysis (as electrooxidation, EO) and photoelectrocatalysis for removing diclofenac (DCF), 15 ppm concentration in 0.1 M NaSO 4 solutions, at different pH conditions (3.0, 6.0 and 9.0) by applying 30 mA cm -2 . Titania nanotubes (TiO 2 NTs)-based materials were prepared to synthetize with a massive PbO 2 deposit on this support to obtain TiO 2 NTs/PbO 2 and a TiO 2 NTs:PbO 2 material consisting in a dispersed PbO 2 deposit on TiO 2 -NTs that allowed the formation of a heterostructured surface of combined composition (TiO 2 and PbO 2 ). Organics removal (DCF and byproducts) was monitored through UV-vis spectrophotometry and high-performance liquid chromatography (HPLC) during degradation tests. TiO 2 NTs/PbO 2 electrode was tested in both processes, removing DCF at neutral and alkaline solution conditions in EO while an unimportant photoactivity was registered at this material. Conversely, TiO 2 NTs:PbO 2 was used as electrocatalytic material in EO experiments, achieving more than 50% of DCF removal at pH 6.0 by applying 30 mA cm -2 . Also, for first time, the synergic effect was investigated when it was exposed to UV irradiation in photoelectrocatalytic experiments, enhancing its efficacy (⁓more than 20%) to remove DCF from a solution with 15 ppm over performance removals achieved (56%) when EO was applied under similar conditions. Chemical Oxygen Demand (COD) analyses showed that significantly higher DCF degradation is reached under photoelectrocatalysis, since COD values decrease a 76% against a 42% decrease achieved with electrocatalysis. Scavenging experiments showed a significant participation on the pharmaceutical oxidation process through the generation of photoholes (h + ), hydroxyl radicals and sulfate-based oxidants., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Monica Cerro-Lopez reports financial support was provided by Universidad de las Américas Puebla. Carlos Alberto Martinez-Huitle reports financial support was provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil. Monica Cerro-Lopez reports a relationship with Consejo Nacional de Ciencia y Tecnología, Mexico that includes: funding grants and travel reimbursement., (Copyright © 2023 Elsevier Inc. All rights reserved.)

As surface-enhanced Raman spectroscopy (SERS) continues developing to be a powerful analytical tool for several probes, four important aspects to make it more accessible have to be addressed: low-cost, reproducibility, high sensibility, and recyclability. Titanium dioxide nanotubes (TiO 2 NTs) prepared by anodization have attracted interest in this field because they can be used as safe solid supports to deposit metal nanoparticles to build SERS substrate nanoplatforms that meet these four desired aspects. TiO 2 NTs can be easily prepared and, by varying different synthesis parameters, their dimensions and specific features of their morphology can be tuned allowing them to support metal nanoparticles of different sizes that can achieve a regular dispersion on their surface promoting high enhancement factors (EF) and reproducibility. Besides, the TiO 2 photocatalytic properties enable the substrate's self-cleaning property for recyclability. In this review, we discuss the different methodological strategies that have been tested to achieve a high performance of the SERS substrates based on TiO 2 NTs as solid support for the three main noble metal nanoparticles mainly studied for this purpose: Ag, Au, and Pt.

Functionalized carbon nanospheres have been synthesized in situ via a facile chemical vapor deposition strategy, fabricated by the pyrolysis of toluene/ethanol mixtures at different percentages (0, 1, 2, 3, 4, and 5 wt% of ethanol). The as-grown nanospheres have been characterized using transmission electron microscopy, scanning electron microscopy, Raman and Fourier transform infrared spectroscopy, x-ray diffraction, nitrogen adsorption, zeta potential measurements and x-ray photoelectron spectroscopy. Results indicate that the incorporation of ethanol in the precursor solution reflected in the presence of oxygen and hydrogen functional groups, the highest functionalized nanospheres without compromising the morphology of the sample were yielded at 3 wt% concentration. These in situ added functional groups rendered the carbon nanostructures enhancedly dispersible and stable in water, avoiding post-synthesis and harsh chemicals processing; envisaging thus applications of the nanospheres in the biomedical field where hydrophilicity of the nanomaterials is mandatory.

Graphene oxide (GO) has lately become an interesting biomaterial due to its stunning properties and versatility, its claimed antimicrobial activity holds promise for potential health applications. Nonetheless, multiple reports investigating GO antibacterial activity lack rigor and uniformity on several aspects which are crucial when evaluating this effect. In this work, we highlight and address these parameters: morphology of the materials, exposure time, exposure methodology and concentration. We investigate the effect of GO and GO-based metallic composites observing these parameters on two pathogenic bacteria. Our nanomaterials have been characterized by means of SEM, EDX, DLS, FTIR and Raman spectroscopies. Escherichia coli and Salmonella Typhimurium suspended in saline solutions (no growth medium) have been exposed to GO (lateral size = 100 nm), silver nanoparticles, ceria nanoparticles, GO/silver and GO/ceria aqueous solutions for 0, 5, 15, 30, 60 and 90 minutes, before plating. Our experiments indicate that no prior exposure of the materials to bacteria (0 min) results in poor inactivation rates independently of concentration, while increasing times of interaction enhance inactivation. Moreover, our experiments show concentration-dependent results showing higher activity for concentrations of 100 μg mL -1 ; and prove that 30 minutes of exposure are sufficient to deploy the antimicrobial effects of these materials. GO possesses the lowest inactivation rate, and the presence of silver and ceria nanoparticles in the GO surface boosts its antimicrobial effect. Thus, the enhancement of the antibacterial activity of graphene oxide relies on 30 minutes of interaction in water, concentration of 100 μg mL -1 , and its decoration by silver/ceria nanoparticles., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Background: Driven by the potential biological applications of graphene, many groups have studied the response of cells exposed to graphene oxide (GO). In particular, investigations of bacteria indicate that there are 2 crucial parameters, which so far have only been investigated separately: GO size and exposure methodology. Our study took into account both parameters. We carefully characterized the samples to catalog sizes and structural properties, and tested different exposure methodologies: exposure in saline solution and in the presence of growth media. Furthermore, we performed experiments with peripheral blood mononuclear cells exposed to our GO materials., Methods: Atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were used to characterize the morphology and composition of different samples of GO: GO-H2O, GO-PBS and GO-MG. Our samples had 2D sizes of ~100 nm (GO-H2O and GO-PBS) and >2 µm (GO-MG). We tested antibacterial activity and cytotoxicity toward peripheral blood mononuclear cells of 3 different GO samples., Results: A size-dependent growth inhibition of Escherichia coli (DH5 α) in suspension was found, which proved that this effect depends strongly on the protocol followed for exposure. Hemocompatibility was confirmed by exposing peripheral blood mononuclear cells to materials for 24 hours; viability and apoptosis tests were also carried out., Conclusions: Our experiments provide vital information for future applications of GO in suspension. If its antibacterial properties are to be potentiated, care should be taken to select 2D sizes in the micrometer range, and exposure should not be carried out in the presence of grow media.

Graphene has emerged as a promising material for infrared (IR) photodetectors and plasmonics. In this context, wafer scale epitaxial graphene on SiC is of great interest in a variety of applications in optics and nanoelectronics. Here we present IR reflectance spectroscopy of graphene grown epitaxially on the C-face of 6H-SiC over a broad optical range, from terahertz (THz) to mid-infrared (MIR). Contrary to the transmittance, reflectance measurements are not hampered by the transmission window of the substrate, and in particular by the SiC Reststrahlen band in the MIR. This allows us to present IR reflectance data exhibiting a continuous evolution from the regime of intraband to interband charge carrier transitions. A consistent and simultaneous analysis of the contributions from both transitions to the optical response yields precise information on the carrier dynamics and the number of layers. The properties of the graphene layers derived from IR reflection spectroscopy are corroborated by other techniques (micro-Raman and X-ray photoelectron spectroscopies, transport measurements). Moreover, we also present MIR microscopy mapping, showing that spatially-resolved information can be gathered, giving indications on the sample homogeneity. Our work paves the way for a still scarcely explored field of epitaxial graphene-based THz and MIR optical devices.

Graphene and graphitic nanoribbons possess different types of carbon hybridizations exhibiting different chemical activity. In particular, the basal plane of the honeycomb lattice of nanoribbons consisting of sp(2)-hybridized carbon atoms is chemically inert. Interestingly, their bare edges could be more reactive as a result of the presence of extra unpaired electrons, and for multilayer graphene nanoribbons, the presence of terraces and ripples could introduce additional chemical activity. In this study, a remarkable irreversibility in adsorption of CO(2) and H(2)O on graphitic nanoribbons was observed at ambient temperature, which is distinctly different from the behavior of nanoporous carbon and carbon blacks. We also noted that N(2) molecules strongly interact with the basal planes at 77 K in comparison with edges. The irreversible adsorptions of both CO(2) and H(2)O are due to the large number of sp(3)-hybridized carbon atoms located at the edges. The observed irreversible adsorptivity of the edge surfaces of graphitic nanoribbons for CO(2) and H(2)O indicates a high potential in the fabrication of novel types of catalysts and highly selective gas sensors.

The current status of graphene edge fabrication and characterization is reviewed in detail. We first compare different fabrication methods, including the chemical vapor deposition method, various ways of unzipping carbon nanotubes, and lithographic methods. We then summarize the different edge/ribbon structures that have been produced experimentally or predicted theoretically. We discuss different characterization tools, such as transmission electron microscopy and Raman spectroscopy, that are currently used for evaluating the edge quality as well as the atomic structures. Finally, a detailed discussion of defective and folded edges is also presented. Considering the short history of graphene edge research, the progress has been impressive, and many further advances in this field are anticipated.

Here we report the synthesis of single-walled carbon nanotube bundles by chemical vapor deposition in the presence of electron donor elements (N, P, and Si). In order to introduce each dopant into the graphitic carbon lattice, different precursors containing the doping elements (benzylamine, pyrazine, triphenylphosphine, and methoxytrimethylsilane) were added at various concentrations into ethanol/ferrocene solutions. The synthesized nanotubes and byproduct were characterized by electron microscopy and Raman spectroscopy. Our results reveal intrinsic structural and electronic differences for the N-, P-, and Si- doped nanotubes. These tubes can now be tested for the fabrication of electronic nanodevices, and their performance can be observed.

We found that multiwalled carbon nanotubes (MWNTs) can be opened longitudinally by intercalation of lithium and ammonia followed by exfoliation. Intercalation of open-ended tubes and exfoliation with acid treatment and abrupt heating provided the best results. The resulting material consists of: (i) multilayered flat graphitic structures (nanoribbons), (ii) partially open MWNTs, and (iii) graphene flakes. We called the completely unwrapped nanotubes ex-MWNTs, and their large number of edge atoms makes them attractive for many applications.

Graphene nanoribbons can exhibit either quasi-metallic or semiconducting behavior, depending on the atomic structure of their edges. Thus, it is important to control the morphology and crystallinity of these edges for practical purposes. We demonstrated an efficient edge-reconstruction process, at the atomic scale, for graphitic nanoribbons by Joule heating. During Joule heating and electron beam irradiation, carbon atoms are vaporized, and subsequently sharp edges and step-edge arrays are stabilized, mostly with either zigzag- or armchair-edge configurations. Model calculations show that the dominant annealing mechanisms involve point defect annealing and edge reconstruction.

Owing to their influence on electrons and phonons, defects can significantly alter electrical conductance, and optical, mechanical and thermal properties of a material. Thus, understanding and control of defects, including dopants in low-dimensional systems, hold great promise for engineered materials and nanoscale devices. Here, we characterize experimentally the effects of a single defect on electrons and phonons in single-wall carbon nanotubes. The effects demonstrated here are unusual in that they are not caused by defect-induced symmetry breaking. Electrons and phonons are strongly coupled in sp(2) carbon systems, and a defect causes renormalization of electron and phonon energies. We find that near a negatively charged defect, the electron velocity is increased, which in turn influences lattice vibrations locally. Combining measurements on nanotube ensembles and on single nanotubes, we capture the relation between atomic response and the readily accessible macroscopic behaviour.

We report the use of chemical vapor deposition (CVD) for the bulk production (grams per day) of long, thin, and highly crystalline graphene ribbons (<20-30 microm in length) exhibiting widths of 20-300 nm and small thicknesses (2-40 layers). These layers usually exhibit perfect ABAB... stacking as in graphite crystals. The structure of the ribbons has been carefully characterized by several techniques and the electronic transport and gas adsorption properties have been measured. With this material available to researchers, it should be possible to develop new applications and physicochemical phenomena associated with layered graphene.