Photoacoustic detection of transient phase transformation of nanoparticles.

The controllable preparation of spherical micro/nano particles of various materials has been achieved via the technology of the laser synthesis and processing of colloids (LSPC) recently. However, there is limited in situ research on the evolution processes of nanoparticles in photothermal transient environments, such as solid-state crystal transformations and changes of state, which limits the understanding and application of LSPC. Photoacoustic (PA) signals are sensitive to the optical, thermal and elastic properties of the medium, and can be used to measure the thermal and spectroscopic properties of matter. In this paper, the PA signals generated by the interaction of the laser with the surrounding liquid medium (ethanol, water, glycerin, etc.) and nanoparticles (Ag, TiO2, CeO2, ZrO2, etc.) are studied when the tunable LSPC technique provides different photothermal conditions (such as thermal expansion, solid crystal transformation and evaporation). It is found that semiconductors with different bandgaps, as light absorbers, have the ability to selectively absorb laser beams of different wavelengths. By changing the wavelength, the PA intensity can be adjusted accordingly. In addition, based on the fast laser heating and tunable fluence characteristics of non-focused laser beams in LSPC technology, transient processes such as material phase transitions and changes of state can be excited separately by adjusting the laser fluence. Taking titanium dioxide as an example, the PA signals generated by laser selective excitation of A-R (anatase into rutile) phase transitions and rutile vaporization can be detected.

Laser-Generated Supranano Liquid Metal as Efficient Electron Mediator in Hybrid Perovskite Solar Cells.

Creating colloids of liquid metal with tailored dimensions has been of technical significance in nano-electronics while a challenge remains for generating supranano (<10 nm) liquid metal to unravel the mystery of their unconventional functionalities. Present study pioneers the technology of pulsed laser irradiation in liquid from a solid target to liquid, and yields liquid ternary nano-alloys that are laborious to obtain via wet-chemistry synthesis. Herein, the significant role of the supranano liquid metal on mediating the electrons at the grain boundaries of perovskite films, which are of significance to influence the carriers recombination and hysteresis in perovskite solar cells, is revealed. Such embedding of supranano liquid metal in perovskite films leads to a cesium-based ternary perovskite solar cell with stabilized power output of 21.32% at maximum power point tracing. This study can pave a new way of synthesizing multinary supranano alloys for advanced optoelectronic applications.

Correction: Preparation of carbon dots by non-focusing pulsed laser irradiation in toluene.

Correction for 'Preparation of carbon dots by non-focusing pulsed laser irradiation in toluene' by Huiwu Yu et al., Chem. Commun., 2016, 52, 819-822, DOI: .

Correction: Fabrication of metal/semiconductor nanocomposites by selective laser nano-welding.

Correction for 'Fabrication of metal/semiconductor nanocomposites by selective laser nano-welding' by Huiwu Yu et al., Nanoscale, 2017, 9, 7012-7015.

Embedding laser generated nanocrystals in BiVO4 photoanode for efficient photoelectrochemical water splitting.

Addressing the intrinsic charge transport limitation of metal oxides has been of significance for pursuing viable PEC water splitting photoelectrodes. Growing a photoelectrode with conductive nanoobjects embedded in the matrix is promising for enhanced charge transport but remains a challenge technically. We herein show a strategy of embedding laser generated nanocrystals in BiVO4 photoanode matrix, which achieves photocurrent densities of up to 5.15 mA cm-2 at 1.23 VRHE (from original 4.01 mA cm-2) for a single photoanode configuration, and 6.22 mA cm-2 at 1.23 VRHE for a dual configuration. The enhanced performance by such embedding is found universal owing to the typical features of laser synthesis and processing of colloids (LSPC) for producing ligand free nanocrystals in desired solvents. This study provides an alternative to address the slow bulk charge transport that bothers most metal oxides, and thus is significant for boosting their PEC water splitting performance.

In situ construction of hollow carbon spheres with N, Co, and Fe co-doping as electrochemical sensors for simultaneous determination of dihydroxybenzene isomers.

Control of the active sites/centers plays an important role in the design of novel electrode materials with unusual properties and achievement of sensors with high performance. In this study, three-dimensional (3D) freestanding multi-doped hollow carbon spheres (N-Co-Fe-HCS) with a layer thickness of 30 nm, which contained multiple active sites of the heteroatom N and transition metals (Co and Fe), were synthesized via a simple template method (with SiO2 as the template) and cost-efficient in situ self-polymerization, self-adsorption/reduction and carbonization strategies. Moreover, a series of hollow carbon sphere composites of the same family (N-HCS, N-Co-HCS and N-Fe-HCS) were prepared by this sensible process using the same method and precursors but different doping elements. These differences lead to different active sites/centers from hollow carbon spheres and improved electrocatalytic activities for dihydroxybenzene isomers. Furthermore, N-Co-Fe-HCS as an electrochemical sensor exhibited excellent simultaneous qualitative and quantitative determination performance for catechol (CC) and hydroquinone (HQ). The detection limit and the linear range were 75 nmol L-1 and 0.5-500 µmol L-1 for CC and 80 nmol L-1 and 0.5-1500 µmol L-1 for HQ, respectively. The interference from the components coexisting in river water on the detection of CC and HQ was not observed. These results indicate that high-performance electrochemical sensors can be constructed by in situ multi-element doping into electrode materials to achieve multi-active sites.

Determination of Trace Available Heavy Metals in Soil Using Laser-Induced Breakdown Spectroscopy Assisted with Phase Transformation Method.

To detect available heavy metals in soil using laser-induced breakdown spectroscopy (LIBS) and improve its poor detection sensitivity, a simple and low cost sample pretreatment method named solid-liquid-solid transformation was proposed. By this method, available heavy metals were extracted from soil through ultrasonic vibration and centrifuging and then deposited on a glass slide. Utilization of this solid-liquid-solid transformation method, available Cd and Pb elements in soil were detected successfully. The results show that the regression coefficients of calibration curves for soil analyses reach to more than 0.98. The limits of detection could reach to 0.067 and 0.94 ppm for available Cd and Pb elements in soil under optimized conditions, respectively, which are much better than those obtained by conventional LIBS.

Highly crystalline graphitic carbon nitride quantum dots as a fluorescent probe for detection of Fe(III) via an innner filter effect.

Bulk g-C3N4 was transformed into water-soluble graphitic carbon nitride quantum dots (g-CNQDs) via a chemical oxidation and liquid exfoliation process. The g-CNQDs possess a size distribution ranging from 1 to 5 nm (centered at 3 nm), excellent crystallinity, and are water soluble. It is found that Fe(III) ions are adsorbed on the surface of the g-CNQDs via electrostatic interaction, and that the blue fluorescence of the g-CNQDs is reduced by Fe(III) via an inner filter effect. By using the g-CNQDs as a fluorescent probe, Fe(III) can be determined at excitation/emission wavelengths of 241/368 nm in spiked natural water samples within 1 min and with good selectivity over other ions. Response is linear in the 0.2-60 µmol·L-1 Fe(III) concentration range, and the detection limit is 23 nmol·L-1. Graphical abstract Graphitic carbon nitride quantum dots (g-CNQDs) emit blue fluorescence at an excitation wavelength of 241 nm. Fe(III) ions are quickly adsorbed on the g-CNQDs via electrostatic interaction, and fluorescence is quenched due to an inner filter effect.

Constituting fully integrated colorimetric analysis system for Fe(III) on multifunctional nitrogen-doped MoO3/cellulose paper.

Using ammonium molybdate and thiourea as precursors, nitrogen-doped MoO3 was produced by a one-step carbonization and then fixed into the cellulose filter paper (NMCP) with acrylic resin as a fixative. NMCP was designed as a multifunctional nanocomposite, i.e., solid phase adsorbent for Fe(III) preconcentration, photocatalyst for iron species transformation and color interference removal, and colorimetric sensor for Fe(III) determination. After photocatalysis, the complex of Fe-humic substances could be transformed into Fe(III) ions, the interference of colored organic matter (e.g., aqueous humic substance) was removed, Fe(III) was enriched selectively onto NMCP with the coexistence of interference metal ions (e.g. Co(II) and Cd(II)) and then transformed into Fe(II) by hydroxylamine and photoreduction and for colorimetric analysis. The obstacle of o-phenanthroline colorimetric method was overcome. The photodegradation activity of MoO3 was improved 2.02 times by nitrogen doping with the optimal mass ratio, which was also 5.11 times of P25-TiO2. The concentration of Fe(III) on NMCP was quantified by the gray-scale using smart phones and image processing software, without complicated equipment. Based on multifunctional NMCP, a fully integrated visual analysis system was proposed and suitable for the field detection of Fe(III) in natural water. The log-linear calibration curve for Fe(III) was in the range of 0.05-5mg/L with a determination coefficient (R2) of 0.976 and detection limit of 15µg/L.

Fabrication of metal/semiconductor nanocomposites by selective laser nano-welding.

A green and simple method to prepare metal/semiconductor nanocomposites by selective laser nano-welding metal and semiconductor nanoparticles was presented, in which the sizes, phases, and morphologies of the components can be maintained. Many types of nanocomposites (such as Ag/TiO2, Ag/SnO2, Ag/ZnO2, Pt/TiO2, Pt/SnO2, and Pt/ZnO) can be prepared by this method and their corresponding performances were enhanced.

Spectral Interference Elimination in Soil Analysis Using Laser-Induced Breakdown Spectroscopy Assisted by Laser-Induced Fluorescence.

The complex and serious spectral interference makes it difficult to detect trace elements in soil using laser-induced breakdown spectroscopy (LIBS). To address it, LIBS-assisted by laser-induced fluorescence (LIBS-LIF) was applied to selectively enhance the spectral intensities of the interfered lines. Utilizing this selective enhancement effect, all the interference lines could be eliminated. As an example, the Pb I 405.78 nm line was enhanced selectively. The results showed that the determination coefficient (R2) of calibration curve (Pb concentration range = 14-94 ppm), the relative standard deviation (RSD) of spectral intensities, and the limit of detection (LOD) for Pb element were improved from 0.6235 to 0.9802, 10.18% to 4.77%, and 24 ppm to 0.6 ppm using LIBS-LIF, respectively. These demonstrate that LIBS-LIF can eliminate spectral interference effectively and improve the ability of LIBS to detect trace heavy metals in soil.

Simultaneous determination of La, Ce, Pr, and Nd elements in aqueous solution using surface-enhanced laser-induced breakdown spectroscopy.

Determination of rare earth elements (REEs) plays an important role in the extraction process. In this work, surface-enhanced laser-induced breakdown spectroscopy (SENLIBS) was introduced to detect REEs (lanthanum, cerium，praseodymium，and neodymium elements) in an aqueous solution. The emission lines of La II 394.91nm, Ce II 418.66nm, Pr II 422.29nm, and Nd II 406.10nm were selected for quantitative analysis by drying the analytical samples on a Zn metal substrate surface and optimizing the experimental parameters. The results showed that the limits of detection (LoDs) for determining La, Ce, Pr, and Nd elements can reach to 0.85, 4.07, 2.97, and 10.98µgmL-1, respectively, which proved that SENLIBS is a feasible method for determining REEs.

Preparation of carbon dots by non-focusing pulsed laser irradiation in toluene.

A simple approach for preparing carbon dots (CDs) by non-focusing pulsed laser irradiation in toluene was presented. The as-prepared CDs were graphite dots, which were formed by ablating the intermediate graphene. The size of the as-prepared CDs could be easily controlled by the input of laser fluence. The mechanism of the photoluminescence was also discussed.