Synthesis, Characterization, Uses and Applications of Porous Clays Heterostructures: A Review.

Porous clay heterostructures (PCH) are obtained by the insertion of an organic bulky cation in the interlayer spacing of a smectite, causing a swelling of the clay mineral. Right after, oxides species, mainly silicon oxide, are incorporated as pillars galleries between adjacent layers to form a porous structure after the removal of the template. The ordering of the clay mineral as well the organic cation incorporated in the synthetic step favors the modulation of the textural properties of the PCH. In addition, the incorporation of heteroatoms in the pillars galleries can also modulate the acidity of the PCH. The modulation of the pore size and the acid properties provides to these materials a wide range of applications in the fields of adsorption and catalysis. This paper carries out a detailed review of the synthesis of PCH, characterization as well as uses and application reported in the literature.

Valorization of wipe wastes for the synthesis of microporous carbons and their application in CO2 capture, gas separation and H2-storage.

Wipe wastes have been used as a cellulosic source to synthesize biochars. Prior to the synthesis of the adsorbents by the pyrolysis of wipes wastes, this waste was treated to remove the pathogenic agents. Then, the wipe wastes were pyrolyzed between 500 and 900 °C to obtain biochars, whose microporosity increased proportionally to the pyrolysis temperature, achieving a maximum CO2-adsorption uptake of 2.53 mmol/g at a pressure of 760 mm of Hg and 25 °C for the biochar pyrolized at 900 °C. The synthesized biochars are also highly selective towards CO2-adsorption in CO2/N2 or CO2/H2 mixtures. Hence, these adsorbents have shown a great potential to be used in flue gas treatment and H2-purification processes. Biochar treatment with KOH further improves microporosity due to chemical activation although the addition of a large amount of KOH leads to excessive microporosity causing a collapse in the pore structure and decreasing CO2-adsorption capacity.

Boosting the electrochemical oxygen reduction activity of hemoglobin on fructose@graphene-oxide nanoplatforms.

A metal-free oxygen reduction reaction (ORR) electrocatalyst with outstanding performance was obtained through an easy and one-pot synthesis of hemoglobin functionalized fructose@graphene-oxide (GO) nanocomposites. The active pyridinic nitrogen sites of the highly unfolded proteins together with the excellent electronic properties of GO appears to be the main factors causing the improved electrocatalytic activity.

Effect of 1-(3-phenoxypropyl) pyridazin-1-ium bromide on steel corrosion inhibition in acidic medium.

The effect of 1-(3-phenoxypropyl) pyridazin-1-ium bromide, a new pyridazinium derivative, on steel corrosion in a HCl (1 M) solution was analyzed using electrochemical impedance and XPS spectroscopy. Experimental results indicated that the inhibition efficiency increased with an increase in an inhibitor concentration. Electrochemical impedance spectroscopy measurements revealed that an increase in the immersion time of steel in an acidic medium from 1 to 12 h and further to 24 h decreased the charge transfer resistance (Rct) and thus decreased the inhibition efficiency. The SEM and XPS analyses linked the inhibition effect to the adsorption of the inhibitor (1-(3-phenoxypropyl) pyridazin-1-ium bromide) on the steel surface.

Gas phase dehydration of glycerol to acrolein over WO3-based catalysts prepared by non-hydrolytic sol-gel synthesis.

Solid acid catalysts based on WO3-SiO2 and WO3-ZrO2-SiO2 were prepared by one-pot non-hydrolytic sol-gel method and tested in the gas phase glycerol dehydration to acrolein. Their structural and textural characteristics were determined by X-ray diffraction (XRD), N2 adsorption, X-ray energy dispersive spectroscopy (XEDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Their acid characteristics were studied by both temperature programmed desorption of ammonia (NH3-TPD) and FTIR of adsorbed pyridine. Under our operating conditions, all the catalysts were active and selective in the transformation of glycerol to acrolein, which was always the main reaction product. The high selectivity to acrolein is achieved on catalysts presenting a higher proportion of Brønsted acid sites. In addition, the role of oxygen in the feed on catalytic performance of these catalysts is also discussed.

Enhanced electrochemical response of carbon quantum dot modified electrodes.

A glassy carbon electrode (GCE) was surface-modified with carbon quantum dots (CQDs) and applied for the effective enhancement of the electrochemical signal for dopamine and uric acid determination. CQDs were prepared from graphite by a green modification of the Hummers method. They were characterized by FTIR-ATR, XPS, solid-state NMR, fluorescence and Raman spectroscopies. TPD-MS analysis was applied to characterize the functionalization of the surface. The CQDs were assembled on the glassy carbon electrode by adsorption because of the large number of carboxy groups on their surface warrants effective adsorption. The modified GCE exhibits a sensitivity that is almost 10 times better than of the bare GCE. The lower limits of detection are 1.3µM for uric acid and 2.7µM for dopamine.

Hydrodechlorination of polychlorinated molecules using transition metal phosphide catalysts.

Ni2P and CoP catalysts (5 wt.% of metal) supported on a commercial SiO2 were tested in the gas phase catalytic hydrodechlorination (HDCl) of mono (chlorobenzene-ClB) and polychlorobenzenes (PCBs) (1,2- dichlorobenzene (1,2-DClB), 1,3-dichlorobenzene (1,3-DClB), 1,4-dichlorobenzene (1,4-DClB), and 1,2,4-trichlorobenzene (1,2,4-TClB)) at atmospheric pressure. It was investigated how the number and position of chlorine atoms in the molecule influence the HDCl activity. The prepared catalysts were characterized by X-ray diffraction (XRD), CO chemisorption, N2 adsorption-desorption at -196°C, and X-ray photoelectron spectroscopy (XPS). Characterization results indicated better active phase dispersion and greater amount of P on the Ni2P catalyst surface. Catalytic results showed that the Ni2P was more active and stable in this type of reactions. The hydrodechlorination activity decreased by increasing the number of chlorine atoms in the molecule and chlorine substituents in close proximity. The observed trend in the HDCl activity was: ClB>1,4-DClB>1,3-DClB>1,2-DClB>1,2,4-TClB. The exception was the catalytic response after 24h on stream observed for the Ni2P in the HDCl reaction of 1,2,4-TClB, which was equal to that observed for the 1,4-DClB molecule, and also yielding benzene as the main reaction product.

Study on the use of 3-aminopropyltriethoxysilane and 3-chloropropyltriethoxysilane to surface biochemical modification of a novel low elastic modulus Ti-Nb-Hf alloy.

A biocompatible new titanium alloy Ti-16Hf-25Nb with low elastic modulus (45 GPa) and the use of short bioadhesive peptides derived from the extracellular matrix have been studied. In terms of cell adhesion, a comparative study with mixtures of short peptides as RGD (Arg-Gly-Asp)/PHSRN (Pro-His-Ser-Arg-Asn) and RGD (Arg-Gly-Asp)/FHRRIKA (Phe-His-Arg-Arg-Ile-Lys-Ala) have been carried out with rat mesenchymal cells. The effect of these mixtures of short peptides have already been studied but there are no comparative studies between them. Despite the wide variety of silane precursors available for surface modification in pure titanium, the majority of studies have used aminosilanes, in particular 3-minopropyltriethoxysilane (APTES). Nevertheless, the 3-chloropropyltriethoxysilane (CPTES) is, recently, proposed by other authors. Unlike APTES, CPTES does not require an activation step and offers the potential to directly bind the nucleophilic groups present on the biomolecule (e.g., amines or thiols). Since the chemical surface composition of this new alloy could be different to that pure titanium, both organosilanes have been compared and characterized by means of a complete surface characterization using contact angle goniometry and X-ray photoelectron spectroscopy.

Fluorescent sensor for Cr(VI) based in functionalized silicon quantum dots with dendrimers.

Highly luminescent nanoparticles based in Silicon quantum dots, coated by hydroxyl PAMAM dendrimer (PAMAM-OH) of 5th generation, were obtained by one step process by hydrothermal treatment of 3-Aminopropyl)triethoxysilane (APTES) in aqueous solution. Previous to the optimization of the synthesis procedure, different dendritic molecules of 5th generation were tested to obtain the most intense fluorescence signal. The influence of different parameters such ratio APTES/PAMAM-OH, pH and ionic strength on the fluorescence intensity was studied. The fluorescence spectra showed maximum excitation and emission wavelengths at 370 and 446 nm, respectively. The obtained silicon nanoparticles (SiQDs@PAMAM-OH) were characterized by TEM, DLS and XPS, and were found to detect selectively Cr(VI) in aqueous solutions at 2.7 µM level of detection, sensitivity of 0.2 µM with a RSD of 0.16% (n=10). To study the feasibility of the proposed system for Cr(VI) detection, it was tested in real electrochemical solution bath and a tanning effluent obtained from electrochemical industry and with two certified waters, demonstrating promising outcomes as nano-sensor.

Fluorescent chemosensor for pyridine based on N-doped carbon dots.

Fluorescent carbon dots (CDs) and its nitrogen doped (N-CDs) nanoparticles have been synthesized from lactose as precursor using a bottom-up hydrothermal methodology. The synthesized nanoparticles have been characterized by elemental analysis, FTIR, Raman, TEM, DLS, XPS, and steady-state and life-time fluorescence. The synthesized carbon nanoparticles, CDs and N-CDs, have a size at about 7.7±2.4 and 50±15nm, respectively, and quantum yields of 8% (CDs) and 11% (N-CDs). These techniques demonstrated the effectiveness of the synthesis procedure and the functionalization of the CDs surface with amine and amide groups in the presence of NH3 in aqueous media. The effect of excitation wavelength and pH on the luminescent properties was studied. Under the optimal conditions, the nitrogen doped nanoparticles can be used as pyridine sensor in aqueous media because they show an enhancement of its fluorescence with a good linear relationship. The analytical method is simple, reproducible and very sensitive for pyridine determination.

Microwave-assisted synthesis of carbon dots and its potential as analysis of four heterocyclic aromatic amines.

Fluorescent water soluble carbon nanoparticles, in short carbon dots (CDs), was synthesized from lactose by microwave assisted hydrochloric acid method. Characterized by TEM and DLS to obtain the morphology shape (average 10nm in size), with a higher negative surface charge supported by the composition was obtained by XPS spectroscopy. The maximum of the emission was centered at 450 nm with a lifetime of 2.1 ns. Without further functionalization of the CDs a nanosensor was obtained that responded exponentially to HAAs in the 0.35-0.45 mg L(-1) concentration range by fluorescence static quenching, demonstrated by the lifetime analysis of the CDs in presence of HAAs. Some amino compounds were selected as model for interferences to evaluate the selectivity of this method, showing a notorious added value, with recoveries around 98%. The accuracy of the method was in terms of RSD about 2.5%. The results suggest their promising applications in chemical sensing.

Effect of hydration of polyamide membranes on the surface electrokinetic parameters: surface characterization by x-ray photoelectronic spectroscopy and atomic force microscopy.

The surface and the solid/liquid interface of two polyamide membranes, one experimental (B0) and one commercial (NF45), have been characterized by X-ray photoelectronic spectroscopy (XPS), atomic force microscopy (AFM), and zeta potential, respectively. The surface roughness, determined by AFM data analysis, is different for the two membranes, and results show that the commercial NF45 membrane presents a much lower roughness than the experimental B0 membrane. XPS data indicate that the surface of membrane NF45 is similar to that of pure polyamide, while membrane B0 contains a considerable amount of impurities. The homogeneity in depth of both membranes was also studied by determining the composition profile at different analysis angles. Streaming potential along the membrane surface or tangential streaming potential (TSP) measurements with NaCl solutions at different concentrations were carried out with both membranes to determine the zeta potential and the electrokinetic surface charge density, and a correlation between membrane surface and interface parameters is made. Some differences in atomic concentrations of membrane surface elements and X-ray photoelectronic spectra of the samples used in TSP measurements and after a drying process at 90 degrees C for 24 h can be observed when they are compared with those for fresh membranes. Electrokinetic parameters for membrane NF45 (TSP, zeta potential, and surface electrokinetic charge density) obtained from three different series of measurements strongly decrease as a result of membrane use, but for membrane B0 they are practically independent of the number of measurements. This difference in the electrokinetic behavior of the two membranes has been related to the hydration process of the surface for each sample studied by XPS and AFM.

Carbon dots obtained using hydrothermal treatment of formaldehyde. Cell imaging in vitro.

Highly photoluminescent carbon dots have been prepared in a one step procedure by hydrothermal treatment of formaldehyde at 180 °C. They show green fluorescence under UV light exposure and emission spectra are centered at 440 nm. Fluorescence lifetimes comprise between 0.7 and 2.70 ns, when the synthesis process lasted for 1-7 days. TEM images of nanoparticles showed a homogeneous size/shape distribution. When the thermal treatment process was carried out for a long time (30 days) formation of aggregates occurred. Carbon dots were further analyzed using (1)H and (13)C-NMR, Raman and FTIR spectroscopy techniques and XPS. Cell imaging of nanoparticles was carried out by using mouse MC3T3-E1 pre-osteoblasts as a model. The nanoparticles were selectively localized in the cytoplasm without further functionalization and could be realized by cellular phagocytosis, so that the fluorescence of these can be used for live cell imaging in vitro.

Gas phase catalytic hydrodechlorination of chlorobenzene over cobalt phosphide catalysts with different P contents.

The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene (CB) at atmospheric pressure was investigated over silica-supported cobalt and cobalt phosphide catalysts containing different P loading and a fixed amount of cobalt (5 wt.%). The effect of the initial P/Co molar ratio on the stoichiometry of the cobalt phosphide phase, the acidity and the hydrogen activation capability were discussed and these properties correlated with the catalytic activity. Catalytic results indicated that the cobalt phosphide phase is much more active than the monometallic cobalt one. The activity raised with the P content present in the sample due to the formation of the CoP phase instead of the Co2P one, which favored the formation of hydrogen spillover species, increased the amount of weak acid sites and the number of exposed superficial cobalt atoms probably related to a better dispersion of the active phase. All the catalysts gave rise benzene as the main reaction product.

Hybrid porous phosphate heterostructures as adsorbents of Hg(II) and Ni(II) from industrial sewage.

Porous phosphate heterostructures (PPH), functionalized with different ratios of aminopropyl and mercaptopropyl groups, labelled as N(x=5,25,50)-PPH and S(x=5,25,50)-PPH, respectively, were tested as adsorbents for Ni(II) and Hg(II) found in industrial sewage from electroplating processes and button battery recycling. X-ray diffraction was used to study the structures. The specific surface area of the pristine material (PPH) was 620 m(2)g(-1), whereas the specific surface areas of the modified mercaptopropyl (S(5)-PPH) and aminopropyl (N(5)-PPH) were 472 and 223 m(2)g(-1), respectively. The adsorption data were fitted to a Langmuir isotherm model. The S(5)-PPH material was saturated by 120 mmol Hg(II) per 100g of material, whereas for Ni(II) adsorption, N(25)-PPH material displayed the highest adsorption with a saturation value of 43.5 mmol per 100g. These results suggest that functionalized PPH materials may be promising toxic metal scavengers and that they may provide an alternative environmental technology.

Application of porous phosphate heterostructure materials for gas separation.

In this study, the adsorbents Cu+-3SiPPH723 and Cu2+-3SiPPH723 were prepared starting from a silica-expanded zirconium phosphate heterostructure, 3SiPPH(0.2), which was subjected to an ion exchange with Cu(I) and Cu(II). These materials were characterized using powder X-ray diffraction, X-ray photoelectron spectroscopy, ammonia thermally programmed desorption, hydrogen temperature-programmed reduction, and N2 adsorption (77 K). The equilibria and kinetics of adsorption of pure propylene (C3H6) and propane (C3H8) were studied using a conventional glass high-vacuum volumetric device, equipped with grease-free valves, in the temperature range of 273-393 K. The starting material, 3SiPPH(0.2), presented a high acidity and irreversible chemisorption of the olefin, which increases with temperature. Unlike the support, the irreversible adsorption of the olefin on the Cu+-3SiPPH723 and Cu2+-3SiPPH723 samples decreases with increasing temperature and disappears at 393 K, showing a very high selectivity toward propylene. The C3H8 adsorption in all the samples was always reversible. On the basis of the results of this study, both Cu+-3SiPPH723 and Cu2+-3SiPPH723 samples can be efficiently applied in the separation of a C3H6/C3H8 mixture at 393 K. Cu+-3SiPPH723 would have the highest efficiency, because its capacity for C3H6 adsorption was higher than that for the Cu2+-3SiPPH723 sample.