Dispersed In N,N-dimethylformamide Research Articles

CuInSe2 quantum dots doped MAPbI3 films with reduced trap density for perovskite solar cells

The organic-inorganic halide perovskite (OIHP) materials are becoming promising, but there is still inherent defect-mediated-carrier recombination in hybrid perovskite materials, thus, leading to inefficient power conversion efficiency (PCE). The defect states, which act as the recombination centers, are usually formed during crystallization process. Here, by a hot injection method, Na2S ligand exchange is applied to synthesize copper indium selenium quantum dots (CuInSe2 QDs), which are well dispersed in N,N-dimethylformamide (DMF) and then added into perovskite precursor solution. The resulted QD-in-perovskite structure is found to be beneficial for enlarging grain size, and thus exhibits an improved crystallinity and absorption due to the passivation of trap states. Hence, the perovskite solar cell (PSC) based on the MAPbI3-CuInSe2 QD hybrid film show an improved carrier lifetime from 58.17 ns to 243.23 ns and an enhanced PCE from 16.3% to 18.4% due to higher open-circuit voltage, compared to the cell device based on the pure perovskite film. Additionally, the optimized cell device presents better stability, which can still keep 75% of the initial PCE after 20-day storage. Such a simple Na2S ligand exchange to introduce QD into perovskite provides strong potential for preparing other hybrid materials.

TiO2 reduction by laser ablation in N,N-dimethyl formamide solvent and their photothermal properties

In this work, reduced Titania (TiO2−x) was obtained by laser ablation of commercial rutile TiO2 powder dispersed in N,N-dimethyl formamide (DMF) using a pulsed Nd:YAG (Neodymium-doped Yttrium Aluminium Garnet) laser (532 nm, 10 ns, 10 Hz). It was observed that DMF solvent was able to promote change in the optical band gap of commercial TiO2 (P25). The Ultraviolet–Visible (UV–vis) absorption measurement showed a shoulder in the infrared region with maximum at 690 nm, characteristic of reduced metal oxide. The electron paramagnetic resonance (EPR) measurements confirmed the presence of oxygen vacancies by the characteristic signal in g = 2.002 g and more intense than water-reduced oxide commonly obtained in other works. The X-ray diffraction (XRD) results show the same crystalline phase to P25 and small shifts due to presence of vacancy’s distorting the TiO2 structure. Scanning electron microscopy (SEM) image have shown surface coalesced particles in comparison to commercial P25, agreeing with nitrogen adsorption measurements which indicated a decrease in the surface area from 10.6 to 6.9 m2/g. The photothermal conversion properties was investigated and the reduced TiO2 samples showed higher temperatures when excited with a laser 785 nm wavelength in function of the strong absorption band and higher vacancy’s concentration.

Functionalization of MXene Nanosheets for Polystyrene towards High Thermal Stability and Flame Retardant Properties.

Fabricating high-performance MXene-based polymer nanocomposites is a huge challenge because of the poor dispersion and interfacial interaction of MXene nanosheets in the polymer matrix. To address the issue, MXene nanosheets were successfully exfoliated and subsequently modified by long-chain cationic agents with different chain lengths, i.e., decyltrimethylammonium bromide (DTAB), octadecyltrimethylammonium bromide (OTAB), and dihexadecyldimethylammonium bromide (DDAB). With the long-chain groups on their surface, modified Ti3C2 (MXene) nanosheets were well dispersed in N,N-dimethylformamide (DMF), resulting in the formation of uniform dispersion and strong interfacial adhesion within a polystyrene (PS) matrix. The thermal stability properties of cationic modified Ti3C2/PS nanocomposites were improved considerably with the temperatures at 5% weight loss increasing by 20 °C for DTAB-Ti3C2/PS, 25 °C for OTAB-Ti3C2/PS and 23 °C for DDAB-Ti3C2/PS, respectively. The modified MXene nanosheets also enhanced the flame-retardant properties of PS. Compared to neat PS, the peak heat release rate (PHRR) was reduced by approximately 26.4%, 21.5% and 20.8% for PS/OTAB-Ti3C2, PS/DDAB-Ti3C2 and PS/DTAB-Ti3C2, respectively. Significant reductions in CO and CO2 productions were also obtained in the cone calorimeter test and generally lower pyrolysis volatile products were recorded by PS/OTAB-Ti3C2 compared to pristine PS. These property enhancements of PS nanocomposites are attributed to the superior dispersion, catalytic and barrier effects of Ti3C2 nanosheets.

Influence of sample depletion on Z-scan measurements of hydroxyl groups modified multi-walled carbon nanotubes dispersions

Hydroxyl groups modified multi-walled carbon nanotubes (MWNTs-OH) were dispersed in N, N-dimethylformamide (DMF), water and chloroform, respectively. Each kind of dispersions were poured in 1-mm, 2-mm and 5-mm quartz cuvettes, respectively. The nonlinear optical (NLO) and optical limiting properties of the dispersions were studied using open-aperture Z-scan technique at 532 nm in nanosecond regime. Results show that thick cuvette or solvents with excellent thermodynamic parameters allows efficient replenishment of MWNTs-OH in the intensely irradiated volume, leading to excellent optical limiting properties arising from the well known nonlinear scattering, while thin cuvette or solvents with poor thermodynamic parameters allows inefficient replenishment of MWNTs-OH, which even leads to false appearance of ‘saturable absorption-like’ or ‘nonlinear refraction-like’ behavior due to the depletion of the sample. The different replenishment efficiency of the dispersions with the same solvent in cuvettes of different thickness can be attributed to the different influence of viscous force near the cuvette sidewalls. This influence should also be noted in other nanomaterials sharing similar NLO mechanism to carbon nanotubes dispersions during Z-scan experiments.

Tunable Multilayers of Self-Organized Silica Nanospheres by Spin Coating

The coating of fused silica by an organized layer of silica nanospheres (NS) is an important issue for the design of optical and topographic properties especially for lithography techniques such as nanosphere lithography (NSL) or nanosphere photolithography (NSPL). Here, the spin coating of NS dispersed in N,N-dimethylformamide (DMF) is studied. The role of the NS diameter, the spin-coating acceleration, and the volume fraction are the parameters to take into account for the formation and organization of NS in single or double closely packed layers. We propose an explanation for this behavior based on the transition between sedimentation and a viscous regime on the basis of the silica NS organization.

Preparation and properties of cellulose membranes with graphene oxide addition

Abstract The paper presents results of research on the preparation of cellulose membranes with graphite oxide addition (GO/CEL). Initially, a cellulose (CEL) solution in 1-ethyl-3-methylimidazole acetate (EMIMAc) was obtained, to which graphene oxide (GO) dispersed in N,N-dimethylformamide (DMF) was added. From this solution, composite membranes were formed using phase inversion method. It was observed that the GO addition influences the physico-chemical properties of GO/CEL composite membranes, resulting in an increase in their mass per unit area, thickness and density, and a decrease in sorption properties. In addition, the study of transport properties has shown that GO/CEL membranes do not absorb BSA particles on their surface, which prevents the unfavorable phenomenon of fouling. An important feature of the obtained membranes is the specific permeate flux which reaches high values (~124 L/m2×h) at 3.8% of the GO addition to the cellulose matrix.

A luminescent cadmium metal-organic framework with potential detection of nitroaromatic compounds

A novel metal-organic framework (MOF) [Cd3(L)2(μ2-H2O)2]·(H2O)3 (1) (H3L=5-(4-carboxy-benzylamino)-isophthalic acid), has been successfully synthesized under hydrothermal condition. Single crystal structure analysis reveals that 1 displays a three-dimensional (3D) framework, which represents a rarely obtained (4, 8)-connected topology. The compound exhibits strong fluorescent emission in the solid state at room temperature. Interestingly, the fluorescence of 1 dispersed in N,N-dimethylformamide (DMF) can be selectively and sensitively quenched by nitroaromatic compounds (NACs), which shows that the complex could be a potential fluorescent sensor for detection of these compounds.

Single step synthesis of Au–CuO nanoparticles decorated reduced graphene oxide for high performance disposable nonenzymatic glucose sensor

A nonenzymatic electrochemical glucose sensor was fabricated using gold–copper oxide nanoparticles decorated reduced graphene oxide (Au–CuO/rGO). A novel one step chemical process was employed for the synthesis of nanocomposite. Morphology and crystal planes of the nanocomposite were characterized using high resolution scanning electron microscopy (HRSEM) and X-ray diffraction (XRD) respectively. The Au–CuO/rGO nanocomposite was dispersed in N,N-dimethyl formamide (DMF) and drop-casted on the working area of the indigenously fabricated screen printed electrode (SPE). The sensor showed good electrocatalytic activity in alkaline medium for the direct electrooxidation of glucose with linear detection range of 1μM to 12mM and a lower detection limit of 0.1μM. The sensor exhibited an excellent sensitivity 2356μAmM−1cm−2. Sensor was used for the determination of serum glucose concentration and the results obtained were compared with commercially available test strips.

Pt-CuO nanoparticles decorated reduced graphene oxide for the fabrication of highly sensitive non-enzymatic disposable glucose sensor

Platinum nanocubes and copper oxide nanoflowers decorated reduced graphene oxide (rGO) obtained by one step chemical process. X-ray crystallographic analysis confirms that CuO in monoclinic form and Pt in cubic crystal form. Pt-CuO/rGO nanocomposite dispersed in N,N-dimethylformamide (DMF) was drop casted onto the working electrode of an indigenously fabricated screen printed three electrode system. Oxidation of glucose on the Pt-CuO/rGO nanocomposite modified screen printed electrode (SPE) was occurred at +0.35V. The sensor showed a limit of detection 0.01μM (S/N=3) and very high sensitivity of 3577μAmM−1cm−2 with linear response upto 12mM. The sensor was highly selective to glucose in the presence of commonly interfering species like ascorbic acid (AA), dopamine (DA), uric acid (UA) and acetaminophen. The sensor was employed for the testing of glucose in blood serum and the results obtained were comparable with other standard test methods.

Electrospray Deposition of Carbon Nanotube Thin Films for Flexible Transparent Electrodes

Flexible transparent carbon nanotube (CNT) electrodes were fabricated by electrospray deposition, a large-area scalable and cost-effective process. The carbon nanotubes were dispersed in N,N-dimethylformamide (DMF) and deposited on polyethylene terephthalate (PET) substrates by electrospray deposition process at room temperature and atmospheric pressure. Major process variables were characterized and optimized for the electrospray process development such as electric field between nozzle and substrates, CNT solution flowrate, gap between nozzle and substrates, solution concentration, solvent properties and surface temperature. The sheet resistance of the electrospray deposited CNT films were reduced by HNO3 doping process. 169 Omega/sq sheet resistance and 86% optical transmittance was achieved with low surface roughness of 1.2 nm. The films showed high flexibility and transparency, making them potential replacements of ITO or ZnO in such as solid state lighting, touch panels, and solar cells. Electrospray process is a scalable process and we believe that this process can be applied for large area carbon nanotube film formation.

Ag/lamellar hosts composites: a route to morphology-controllable synthesis of Ag nanoparticles

An easy and novel routine are reported for the preparation of metallic silver nanoparticles (AgNPs) with controlled morphology, using Na+–magadiite swelled with hexadecyltrimethylammonium bromide (CTA+–magadiite) and a layered aluminophosphate with kanemite-type structure modified with n-dodecylammonium and n-butylammonium (but,dod-AlPO-kan) as hosts. For the preparation of the metallic AgNPs (Ag0) in the interlamellar space, the CTA+–magadiite and but,dod-AlPO-kan hosts were dispersed in N,N-dimethylformamide (DMF) solution with different AgNO3 concentrations. DMF acts as reducing agent of Ag+ ions leading to nanoparticles with disk-like morphology of magadiite silicate; these were characterized by TEM and UV–Vis spectroscopy. On the other hand, the AgNPs are intercalated in but,dod-AlPO-kan showing spherical-like morphology. The UV–Vis spectra of the nanocomposites based on Ag0 and magadiite silicate show bands at 565 nm that can be attributed to Ag0 nanodisks. The Ag-but,dod-AlPO-kan-based nanocomposites present a band at 422 nm attributed to the surface plasmon resonance of Ag0 nanospheres. The results of transmission electron microscopy agree very well with XRD and UV–Vis analysis, indicating the formation of AgNPs with different morphologies using the two kinds of lamellar materials. The magadiite host has an important role in the synthesis of Ag nanodisks, because it controls the growth of nanoparticles inside the interlayer region with disk-like morphology due the high interlayer interactions of the silicate, leading to the growth of nanoparticles in only two directions (xy plane). On the other hand, when but,dod-AlPO-kan is used a sphere-like morphology is preferred due the best accommodation of AgNPs between the layers of aluminophosphate host.

Supercritical N,N-dimethylformamide for the exfoliation and phase transition of layered manganese oxide materials to obtain trimanganese tetroxide nanosheets

A novel method using supercritical N,N-dimethylformamide (SC-DMF) exfoliation is proposed for the preparation of trimanganese tetroxide (Mn3O4) nanosheets. The obtained Mn3O4 nanosheets have nanoscale thickness and lateral dimensions of hundreds of nanometers. The change in morphology from a bulk to a two-dimensional structure when exfoliated with SC-DMF is characterised. The exfoliated products can be uniformly dispersed in N,N-dimethylformamide (DMF), the dispersion has a molar extinction coefficient of approximately 5.52 × 102 mol−1 dm3 cm−1 at a peak wavelength of 266 nm. The fourier transform infrared (FTIR) spectra show that intercalation mainly occurs between 300 °C and 400 °C. Raman spectroscopy indicates that the phase transition from MnO2 to Mn3O4 takes place between 200 °C and 400 °C. X-ray diffraction (XRD) confirms that the phase transition between the manganese oxides begins at around 350 °C. The exfoliated products possess strong coercivity, approximately 7 kOe, at low temperatures. It is demonstrated that the exfoliated Mn3O4 products result from exfoliation and phase transition in SC-DMF. The exfoliated nanosheet materials can be easily cracked in the course of exfoliation and aggregate when collected, these phenomena are attributed to the fragility and magnetic properties of the material, respectively.

Poly(ε-caprolactone) reinforced with fibres of Poly(methyl methacrylate) loaded with multiwall carbon nanotubes or graphene nanoplatelets

Aligned electrospun fibres of Poly(methyl methacrylate) (PMMA), either neat, loaded with multiwall carbon nanotubes (MWCNTs) or with graphene nanoplatelets (GNPs) were used as reinforcement of a Poly(ε-caprolactone) (PCL) matrix. Previously to fibre formation, MWCNTs and GNPs were accurately disentangled and dispersed in N,N-Dimethylformamide (DMF) by means of sonication. In some cases sonicated GNPs were further dispersed by centrifugation. All electrospun fibres are uniform and well aligned, with a mean diameter ranging between 1–2μm. PCL films were produced by solvent casting. The composites were manufactured by means of film stacking technique, performed at 90°C for 30min under pressure in order to insure PCL melting and flowing and correct fibre impregnation. In all composites the PCL matrix revealed to be strongly adhered to the fibres. The insertion of PMMA reinforcement leads to an increase in yield stress of the PCL from 5.0±0.1 to 10.4±0.5MPa. The addition of the carbon fillers produces a further slight improvement in the mechanical properties and the best results are obtained for the samples prepared starting from the centrifuged dispersion of GNPs (yield stress=14.0±0.5MPa).

Formation of N-acylureas on the surface of TEMPO-oxidized cellulose nanofibril with carbodiimide in DMF

A method for conversion of carboxyl groups present on the surface of TEMPO-oxidized cellulose nanofibrils to N-acylureas using carbodiimide was developed. A TEMPO-oxidized cellulose nanofibril with free carboxyl groups (TOCN–COOH) dispersed in N,N-dimethylformamide (DMF) is prepared from a bleached kraft pulp, and then the TOCN–COOH is reacted with either N,N′-diisopropylcarbodiimide (DIC) or N,N′-dicyclohexylcarbodiimide (DCC) under apparently homogeneous conditions. FT-IR and solid-state 13C NMR analyses showed that the reaction products contained N-acylurea groups, and yields were >80%. Conversion ratios of carboxyl groups to N-acylureas are approximately 80 and 60%, when DIC and DCC, respectively, of 5 mol per mole of carboxyl groups are used as the reagents. X-ray diffraction analysis demonstrated that neither crystallinity nor crystal width of the original wood cellulose I structure was changed by the N-acylurea formation. The isolated and never-dried TOCN-N-acylureas are nano-dispersed in DMF but not in i-PrOH or dioxane. Pellets of the TOCN-N-acylureas had water-contact angles of >70°.

Fabrication and optical properties of gallium phosphide nanoparticulate thin film

The gallium phosphide (GaP) nanoparticulate thin films were fabricated by colloidal suspensions deposition with GaP nanoparticles dispersed in N, N-dimethylformamide (DMF). The microstructure and optical properties of the film have been studied by scanning electron microscopy, high resolution transmission electron microscope, and optical absorption and fluorescence spectra. The morphology of the film was found to be composed of nanoparticle aggregates, and with an irregularly rough surface. From the result of fluorescence, it can be established that the film not only retains the violet and blue light emissions which ascribed to transition from conduction band to valence band of gallium phosphide particles, but has an excellent luminescence property. The correlation between the optical properties and the microstructure of the thin film is discussed.

Optical limiting and bleaching effects in a suspension of onion-like carbon

We have studied the effect of nanosecond laser pulses (λ = 1064 nm) on the optical properties of onion-like carbon (OLC) prepared by high-temperature vacuum annealing of detonation nanodiamond and dispersed in N,N-dimethylformamide (DMF). The results demonstrate that, under low-intensity irradiation, the OLC suspension displays optical limiting behaviour. Increasing the incident intensity leads to bleaching of the suspension in the visible and near-IR spectral regions.

Functionalization of Multi‐Walled Carbon Nanotubes by Thermo‐Grafting with α‐Methylstyrene‐Containing Copolymers

AbstractThe present article reports on a strategy for the functionalization of multi‐walled carbon nanotubes (MWCNTs) by grafting with various polymer chains. Copolymers consisting of α‐methylstyrene (AMS) and a second monomer, that is glycidyl methacrylate (GMA) or styrene (St), were synthesized in advance. The copolymers were heated in the presence of MWCNTs in solution, decomposition of the AMS sequences occurred, providing macroradicals, which further attacked the double bonds on the MWCNT surfaces. Grafting of the copolymer chains onto the surface of the MWCNTs was thus achieved, as demonstrated by FT‐IR, XPS and Raman technologies. The resulting poly(AMS‐co‐GMA)‐g‐MWCNTs could be uniformly dispersed in N,N‐dimethylformamide (DMF) and acetone, and the poly(AMS‐co‐St)‐g‐MWCNTs also could be uniformly dispersed in DMF.magnified image

Electrophoretic drawing of continuous fibers of single-walled carbon nanotubes

Control over the current during electrophoretic drawing of continuous fibers of single-walled carbon nanotubes (SWCNTs) is shown to be critical in producing long fibers with specific diameters. In the process, as-produced SWCNTs are first dispersed in N,N-dimethylformamide (DMF) by sonication. A tungsten probe tip is then immersed in the SWCNT∕DMF solution, and a dc bias is applied between the tip and another electrode at the bottom of the beaker containing the solution. After a dark cloud several millimeters in diameter develops around the tip, the electrode is withdrawn to form continuous macroscopic fibers of SWCNTs. The resulting fiber length and diameter are found to be principally determined by the magnitude of the current. Under constant voltage conditions where the current is allowed to vary, the fibers are short (several millimeters long) and their diameters vary drastically along their lengths. Of significance is the fact that when the current is maintained at constant values, fibers several centimeters in length with uniform diameters ranging from 26to42μm are obtained at a withdrawal rate of 0.85μm∕s. For this withdrawal rate, long fibers (∼3cm and greater) are obtained at an optimum value of the current (400nA) using hybrid conditions where the voltage is maintained constant earlier in the process while the current is maintained constant later in the process. Control of the total current at low values during this process has the potential to produce long fibers with uniform submicron diameters.

Square Wave Voltammetry Determination of Brucine at Multiwall Carbon Nanotube‐Modified Glassy Carbon Electrodes

In this article, the electrochemical behavior of brucine at the multiwall carbon nanotubes (MWNTs)‐modified glassy carbon electrode (GCE) was studied by cyclic voltammetry (CV) and square wave voltammetry (SWV). The purified MWNTs dispersed in N,N‐dimethylformamide (DMF) were characterized by transmission electron microscopy (TEM). A series of electrochemical parameters of brucine were calculated by chronoamperometry (CA) and chronocoulometry (CC). A better electrochemical response was observed at MWNTs‐modified electrode than the other film‐modified electrodes. Cyclic voltammetric curves showed an irreversible oxidative peak (E pa1 = 937 mV) and a pair of perfect well reversible peaks, ΔE p2 = 13 mV (E pa2 = 418 mV, E pc2 = 405 mV). The second redox peak current of brucine increased linearly with the square root of scan rate in the low range, so it is a diffusion‐controlled process, and the electrocatalytic process mechanism for the brucine was investigated. The SWV currents of brucine at the modified electrode increased linearly with its concentration in the range of 1.0 × 10−6 to 1.0 × 10−4 mol L−1, with a detection limit of 2.0 × 10−7 mol L−1. The MWNTs‐modified electrode can be used to determine brucine in practical samples with satisfactory results. The method is simple, quick, sensitive, and accurate.