Pedro Atienzar

From biomass wastes to large-area, high-quality, N-doped graphene: catalyst-free carbonization of chitosan coatings on arbitrary substrates

Chitosan is a N-containing biopolymer that can form high-quality films on glass, quartz, metals and other hydrophilic surfaces. Pyrolysis of chitosan films under argon at 800 °C and under inert atmosphere gives rise to high-quality single layer N-doped graphene films (over 99% transmittance) as evidenced by XPS, Raman spectroscopy, and TEM imaging.

Preparation of graphene quantum dots from pyrolyzed alginate.

Pyrolysis at 900 °C under an inert atmosphere of alginate, a natural widely available biopolymer, renders a graphitic carbon that upon ablation by exposure to a pulsed 532 nm laser (7 ns, 50 mJ pulse(-1)) in acetonitrile, water, and other solvents leads to the formation of multilayer graphitic quantum dots. The dimensions and the number of layers of these graphitic nanoparticles decrease along the number of laser pulses from 100 to 10 nm average and from multiple layers to few layers graphene (1-1.5 nm thickness), respectively, leading to graphene quantum dots (GQDs). Accordingly, the emission intensity of these GQDs increases appearing at about 500 nm in the visible region along the reduction of the particle size. Transient absorption spectroscopy has allowed detection of a transient signal decaying in the microsecond time scale that has been attributed to the charge separation state.

Hybrid polymer–metal oxide solar cells by in situ chemical polymerization

We present a new approach for improving the infiltration of a conjugated polymer into the pores of a nanostructured metal oxide electrode, whereby the polymer is prepared directly inside the porous oxide film by in situ chemical polymerization. We apply this method to the polymerisation of poly[2-methoxy-5-(2 ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) inside a nanostructured porous TiO2 layer by adapting the synthetic route based on the Gilch reaction. Transient and steady state optical studies show that the light absorption and emission properties of the polymer so produced are similar to those of the polymer synthesised ex situ, while the photoinduced charge separation yield is improved by in situpolymerisation. The photocurrent generated by hybrid polymer/metal oxide solar cells prepared by this methodology is enhanced by a factor of two to three relative to devices prepared with pre-synthesised polymer. The improved photocurrent and charge separation yield for the polymer produced in situ are attributed to improved infiltration of the polymer into the metal oxide film.

Solar energy harvesting in photoelectrochemical solar cells

Here we study different approaches for increasing energy harvesting in titania based photoelectrochemical solar (PES) cells. We study the light harvesting of PES cells when photonic crystal and photonic sponge architectures are used. We also report on the influence of the surface corrugation of the metal electrode on the harvesting of photocarriers in solar cells

Apollony photonic sponge based photoelectrochemical solar cells

We have developed a quasi-fractal colloidal crystal to localize efficiently photons in a very broad optical spectral range; it has been applied to prepare dye sensitized photoelectrochemical solar (PES) cells able to harvest very efficiently photons from the ultraviolet (UV) and the visible (VIS) regions of the solar spectrum.

Hydrotalcites of zinc and titanium as precursors of finely dispersed mixed oxide semiconductors for dye-sensitized solar cells

Hydrotalcites are layered materials whose sheets are constituted by octahedra occupied by two different metals (one divalent and the other tri- or tetravalent) and having oxide or hydroxide at the corners. The excess of positive charge of the sheets is compensated by anions located at the interlamellar space. In the present work we have synthesized two hydrotalcites containing zinc and titanium (Zn/Ti atomic ratio in the gel synthesis 6.25) that differ on the absence or presence of sodium dodecyl sulfate in the interlamellar spaces. Calcination of these hydrotalcites leads to a film of intimately dispersed mixed oxide semiconductor that was used as semiconductor for dye sensitised solar cells. Using a ruthenium polypyridyl complex as dye, two photovoltaic cells constructed by films of mixed oxides derived from hydrotalcite calcination were prepared. The highest efficiency parameters were VOC = 0.63 V, JSC = 2.18 mA cm−2, FF = 0.465, η = 0.64%. These efficiency values are not far from those obtained for an analogous photovoltaic cell prepared using P25 titania.

Photochemistry of single wall carbon nanotubes embedded in a mesoporous silica matrix

By embedding single wall carbon nanotubes in a mesoporous silica matrix (SWNT@SiO2) the photochemical properties have been measured upon laser excitation at 266 nm; the SWNT@SiO2 exhibits long-lived emission (lambda em = 400 nm, tau = 0.95 microsecond), transient absorption (lambda max = 390 nm, tau = 11 microseconds) and is able to generate singlet oxygen in D2O.

Efficiency Records in Mesoscopic Dye‐Sensitized Solar Cells

The aim of the present review article is to show the progress achieved in the efficiency of dye-sensitized solar cells (DSSCs) by evolution in the structure and composition of the dye. After an initial brief description of DSSCs and the operating mechanism the major part of the present article is organized according to the type of dye, trying to show the logic in the variation of the dye structure in order to achieve strong binding on the surface of the layer of nanoparticulate TiO2 , efficient interfacial electron injection between the excited dye and the semiconductor, and minimization of the unwanted dark current processes. Besides metal complexes, including polypyridyls and nitrogenated macro rings, organic dyes and inorganic light harvesters such as quantum dots and perovskites have also been included in the review. The last section summarizes the current state of the art and provides an overview on future developments in the field.

Stimuli-responsive hybrid materials: breathing in magnetic layered double hydroxides induced by a thermoresponsive molecule

A hybrid magnetic multilayer material consisting of CoAl–LDH ferromagnetic layers intercalated with thermoresponsive molecules diluted with a flexible surfactant has been obtained.

Heck reaction on single-walled carbon nanotubes. Synthesis and photochemical properties of a wall functionalized SWNT-anthracene derivative

Sidewall functionalization of single-walled carbon nanotubes (SWNTs) via the Heck cross-coupling reaction of pre-functionalized p-iodophenyl SWNTs allows the covalent binding of different groups such as alkyl chains, dialkylamino or anthracenyl moieties. Functionalized SWNTs were characterized by a set of methods including 1H NMR, ATR-FTIR, XPS, UV/vis and Raman spectroscopic techniques. The degree of functionalization was estimated as 5.5 wt%. Laser flash photolysis studies comparing a covalently bonded anthracenyl derivative and mixtures of anthracene precursor and SWNTs revealed similarities between both systems (occurrence of photoinduced electron transfer, SWNT acting as electron acceptor) and differences (lifetimes of the charge separation), the charge separated state being much shorter lived for the system having covalent bonding with respect to the independent components.