Nanoporous Features Research Articles

Uniform Poly(vinyl ethylene carbonate) based metal-organic framework separator for smooth lithium-ion electrodeposition

Nanoporous feature in Metal-Organic Frameworks (MOFs) could tune Li+-solvated species and provide high potential for stabilizing lithium metal anodes. However, the inevitable voids within MOF crystallites accommodating free liquid electrolyte, which re-solvates Li+-solvated compounds and vanishes nanopores' advantage for controlling Li+-solvates. Herein, we report an in-situ carbonate photopolymerization reaction within MOF channel that constitutes a uniform nanoporous separator (PVEC-MOF) for smoothing Li+ electrodeposition. PVEC-MOF membrane exhibits accelerating lithium-ion conduction and superior electrochemical performance according to the interconnected ionic nano-channels, whose overpotential maintains at about 0.01 V after 600 cycles in Li-symmetric cell without forming lithium dendrite. Furthermore, employing PVEC-MOF separator in high-voltage cathode material (LiNi0.6Co0.2Mn0.2O2) based Li-metal batteries could effectively enhance electrochemical property and prolong cycling lifespan. This work provides a novel strategy to convert traditional MOF family into uniform nanoporous lithium-ion battery separator, which promotes Li+ smooth electrodeposition and inhibits lithium dendrites in high-energy-density lithium-metal batteries.

Stretchable conductors based on nanoporous Ag for flexible sensors

Conductive filler is essential to fabricate stretchable conductors for flexible electronics. In this paper, a novel kind of conductive filler, regularly nanoporous Ag (NP–Ag) is synthesized using a method called “complexation coprecipitation-rapid reduction”, which offers rapid, facile, and environment-friendly advantages. Owing to the nanoporous feature, the as-prepared conductor containing low contents of NP-Ag can exhibit excellent conductivity. Typically, the fluorine rubber-based conductor containing 45 wt% of NP-Ag can maintain a conductivity as high as 1578 S cm−1, while the composite loaded with the same content of fashionable filler (commercial Ag micro-flakes) remains non-conductive. Utilizing this conductor, a strain sensor with excellent sensitivity and repeatability can be fabricated conveniently. The synthetic advantages and regular porosity would make those microstructures a filler candidate for preparing large-area, low-cost, and high-through stretchable conductors.

Advances in nanoporous materials for next-generation battery applications.

In recent years, nanoporous materials, mainly represented by metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have shown unparalleled potential in critical applications such as energy storage, gas separation and catalysis. The integration of MOFs/COFs into battery technology has garnered substantial research attention since it was found that such materials also play important roles in batteries. The highly controllable nanoporous features of MOFs/COFs enable the regulation of the solvation environment of lithium ions, thereby significantly improving the performance of lithium metal batteries. Moreover, the selective adsorption features of MOFs/COFs make them particularly useful for stabilising high nickel cathodes and sulfur cathodes. This review provides an overview of the application of MOFs/COFs in batteries, and explores potential future directions and challenges in this rapidly evolving interdisciplinary field.

Liquid-Metal Solvents for Designing Hierarchical Nanoporous Metals at Low Temperatures.

Metallic nanoarchitectures hold immense value as functional materials across diverse applications. However, major challenges lie in effectively engineering their hierarchical porosity while achieving scalable fabrication at low processing temperatures. Here we present a liquid-metal solvent-based method for the nanoarchitecting and transformation of solid metals. This was achieved by reacting liquid gallium with solid metals to form crystalline entities. Nanoporous features were then created by selectively removing the less noble and comparatively softer gallium from the intermetallic crystals. By controlling the crystal growth and dealloying conditions, we realized the effective tuning of the micro-/nanoscale porosities. Proof-of-concept examples were shown by applying liquid gallium to solid copper, silver, gold, palladium, and platinum, while the strategy can be extended to a wider range of metals. This metallic-solvent-based route enables low-temperature fabrication of metallic nanoarchitectures with tailored porosity. By demonstrating large-surface-area and scalable hierarchical nanoporous metals, our work addresses the pressing demand for these materials in various sectors.

A Protophilic MOF Enables Ni-Rich Lithium-Battery Stable Cycling in a High Water/Acid Content.

Trace protic impurities, such as water and hydrofluoric acid (HF), can severely degrade the stable and long cycling of lithium batteries. Therefore, the costly water removal process is inevitably needed throughout production of lithium batteries, leaving the paradox that energy-saving lithium-battery technology consumes non-negligible amounts of energy. Herein, a unique ionic metal-organic framework (MOF) is reported that enables highly destructive H2 O/HF-tolerant lithium batteries. The isolated ionic fluorine sites in the MOF exhibit unusual protophilicity and efficiently capture ppm-levels H2 O/HF from the highly polar electrolyte solvents. The resulting MOF-based LiNi0.6 Mn0.2 Co0.2 O2 │Li battery achieves over 300 cycles in the presence of 800ppm H2 O or 1107ppm acidic impurity. This tenfold longer battery lifespan relative to those for batteries with conventional standard separators demonstrates its excellent electrochemical cycling performance. The results reveal that the rational use of unique nanoporous features of MOFs can provide new possibilities for long-standing challenges in the lithium-battery industry.

Existence of Ti3+ and dislocation on nanoporous CdO–TiO2 heterostructure applicable for degrading chlorophenol pollutant

This study addresses the significance of wastewater recuperation by a simple and facile treatment process known as photocatalyst technology using visible light. Titanium di-oxide (TiO2) is the most promising photocatalyst ever since longing decades, has good activity under UV light, owing to its small band gap. Hence, TiO2 has been modified with metal oxides for the positive response against visible light. Since this is an efficient process, the novelty has been made on nanometal oxide CdO (cadmium oxide) combined with TiO2 to acquire the best efficiency of degrading organic chlorophenol contaminant. Initially, the composites were synthesized by sol-gel and thermal decomposition methods and investigated for their various outstanding properties. The characterized outcomes have exhibited heterostructures with reduced crystallite size from the X-ray diffraction studies. Then, the determination of nanoporous feature was recognized through HR-TEM analysis which was also detected with some dislocations. The EDX spectrum was identified the perfect elemental composition. The nitrogen adsorption-desorption equilibrium was attained that offers many pores measured with high surface area. The XPS result convinced that Ti3+ was accessible along with TIO2/CdO composite. Further the absorption towards higher wavelength was obtained from UV–vis spectra. Finally, for the photocatalytic application of chlorophenol, the composite shows higher percentage of degrading efficiencies than the pristine TiO2. The photocatalytic mechanism was discussed in detail.

Time-Resolved Characterization of Electrochemically-Induced Solid Oxide Cell Microstructure Evolution

Solid oxide cells (SOC) are exciting both for their capability of fuel-flexible electricity generation and their promise in the production of green H2; however, their degradation and long-term performance remain important questions. Operating individual button cells to characterize these changes is prone to cell-to-cell variations, whereas large-area cell/stack life testing requires considerable resources. In both cases, full cell characterization usually must wait until the completion of the life test, which may delay getting results for months or years. While progress has been made in observing microstructural changes over time (termed here time-resolved characterization) using techniques like non-destructive transmission x-ray microscope tomography, such experiments are difficult to implement, especially the effect of current is unexplored due to geometrical and gas environmental limitations of the system.Presented here is a method to rapidly obtain time-resolved microstructural information of the same cell in tandem with electrochemical measurements. While SOC degradation arises due to a range of processes, this work focuses on the microstructural evolution of Ni-YSZ fuel electrodes that occurs during electrolysis operation, which is known to be a key issue. Two key experimental features allowed time-resolved characterization of multiple cells simultaneously: (1) the use of Ni-YSZ symmetric cells allows multiple cells of different size in a single test by avoiding the need for gas seals, and (2) the use of laser milling to allow controlled removal of a portion of each cell during the test.Here we illustrate the method for the case of low steam content and high current density, designed to exacerbate and accelerate electrolysis degradation due to the highly reducing conditions achieved. Tape-cast planar electrode-supported Ni-YSZ symmetric cells were laser cut into precise geometries with well-defined projected areas and easily removable sections. Four cells with projected areas of 1, 1, 0.75, and 0.5 cm2 were connected in series within the same furnace at 800 C and a gas environment of 97% H2 and 3% H2O. A current of 0.75 A was run through three of the cells, resulting in current densities of 0.75, 1.0, and 1.5 A/cm2, while one was maintained with no current. The life test lasted for 500 h, and the microstructure was observed at 0, 200, and 500 hours.Figure 1 shows the microstructures observed at the highest current density by polished cross-sectional SEM and FIB-polished sections under conditions that provided Ni/YSZ contrast. Microstructural degradation had occurred by 200 h and became immense at 500 h, due to high current density in these reducing conditions. By 200 hours, grain boundaries become enriched with Ni, likely due to the formation of Ni-Zr intermetallics in the ultra-low pO2 induced by local overpotential as reported by Chen[1] and Szasz[2]. Additionally, the electrode-electrolyte interface becomes nanoporous and a Ni enriched fracture is present ~2 μm into the electrolyte. By 500 hours, the Ni rich nanoporosity has progressed more than 10 μm into the electrolyte and created islands of large grains surrounded by Ni-rich deposits.Electrochemical impedance spectroscopy measurements show a clear initial decrease in polarization resistance followed by an overall impedance increase by 200 hours. These correspond to the initial electrochemical boost from the production of a nanoporous structure, followed by the deactivation of areas of the cell due to the large fractures through the electrolyte.[1] M. Chen et al., “Microstructural Degradation of Ni/YSZ Electrodes in Solid Oxide Electrolysis Cells under High Current,” J. Electrochem. Soc., vol. 160, no. 8, pp. F883–F891, 2013, doi: 10.1149/2.098308jes.[2] J. Szász et al., “High-Resolution Studies on Nanoscaled Ni/YSZ Anodes,” Chem. Mater., vol. 29, no. 12, pp. 5113–5123, 2017, doi: 10.1021/acs.chemmater.7b00360.Figure 1: Microstructural and electrochemical changes of a symmetric Ni-YSZ SOC undergoing 1.5 A/cm2 in reducing conditions at 0, 200, and 500 hours. Cathode is on the left in all images; anode is on the right. a, b, c) Backscatter electron imaging reveals destruction of the dense YSZ electrolyte over the lifetime of the experiment. Lines of brighter phases on the anode side of fractures are Ni deposits. d, e, f) Focused Ion Beam cross sections reveal nanoporosity forming in the first 10 μm from the cathode-electrolyte interface at 200 and 500 hours. Charging is evident as a result of curtaining from the nanoporous features in the electrolyte. g) Electrochemical impedance spectroscopy shows the initial decrease in resistance from 0 to 48 hours followed by increasing resistance due to microstructure evolution. Figure 1

Effects of Siliceous Natural Nanomaterials Applied in Combination with Foliar Fertilizers on Physiology, Yield and Fruit Quality of the Apricot and Peach Trees.

Siliceous natural nanomaterials (SNNMs), i.e., diatomaceous earth and natural zeolites, have a nanoporous structure with large active surfaces that adsorb cations or polarized molecules. Such nanoporous feature determines the effects related to SNNM utilization as low-risk plant protectants and soil improvers. This work used SNNMs from Romanian quarries as carriers for foliar fertilizers applied to stone-fruit trees, apricot and peach. We determined the effects of SNNMs on the physiology, yield and fruit quality of the treated stone-fruit trees. SNNM application determined impacts specific to the formation of particle films on leaves: reduced leaf temperature (up to 4.5 °C) and enhanced water use efficiency (up to 30%). Foliar fertilizers’ effects on yield are amplified by their application with SNNMs. Yield is increased up to 8.1% by the utilization of SNNMs with foliar fertilizers, compared to applying foliar fertilizer alone. Diatomaceous earth and natural zeolites promote the accumulation of polyphenols in apricot and peach fruits. The combined application of SNNMs and foliar fertilizer enhance the performance of peach and apricot trees.

Probing the Core–Shell Organization of Nanoconfined Methane in Cylindrical Silica Pores Using In Situ Small-Angle Neutron Scattering and Molecular Dynamics Simulations

Determining the structure of nanoconfined compressed fluids is essential for predicting the fate of these fluids in subsurface geologic formations with nanoporous features and to engineer novel nan...

Second Generation Nanoporous Silicon Nitride Membranes for High Toxin Clearance and Small Format Hemodialysis.

Conventional hemodialysis (HD) uses floor-standing instruments and bulky dialysis cartridges containing ≈2 m2 of 10 micrometer thick, tortuous-path membranes. Portable and wearable HD systems can improve outcomes for patients with end-stage renal disease by facilitating more frequent, longer dialysis at home, providing more physiological toxin clearance. Developing devices with these benefits requires highly efficient membranes to clear clinically relevant toxins in small formats. Here, the ability of ultrathin (<100 nm) silicon-nitride-based membranes to reduce the membrane area required to clear toxins by orders of magnitude is shown. Advanced fabrication methods are introduced that produce nanoporous silicon nitride membranes (NPN-O) that are two times stronger than the original nanoporous nitride materials (NPN) and feature pore sizes appropriate for middle-weight serum toxin removal. Single-pass benchtop studies with NPN-O (1.4 mm2 ) demonstrate the extraordinary clearance potential of these membranes (105 mL min-1 m-2 ), and their intrinsic hemocompatibility. Results of benchtop studies with nanomembranes, and 4 h dialysis of uremic rats, indicate that NPN-O can reduce the membrane area required for hemodialysis by two orders of magnitude, suggesting the performance and robustness needed to enable small-format hemodialysis, a milestone in the development of small-format hemodialysis systems.

First-Principles Design of Cu12shellFecore Core–Shell Clusters Assembled with K3O into Hexameric Rings: Implications for Gas-Storage Materials

Material design using cluster assembly is performed using Cu12shellFecore and K3O clusters as building blocks. The Cu12shellFecore cluster has an icosahedral structure. Six Cu12shellFecore clusters are aligned in a hexagonal shape, while the K3O clusters are applied as binders. The electronic structure of [Cu12FeK3O]6 reveals that the O atom in K3O acts as a glue for connecting Cu12Fe clusters together, while the K atom in the K3O clusters acts as a separator for preventing unwanted interaction of the Cu12Fe clusters. [Cu12FeK3O]6 is designed and has potential application in gas storage because of their nanoporous features.

Multiple diffusion mechanisms of shale gas in nanoporous organic matter predicted by the local diffusivity lattice Boltzmann model

Shale gas diffusion properties in organic matter (OM) are crucial for estimating gas yield. The gas diffusion process involves multiple diffusion mechanisms namely molecular diffusion, Knudsen diffusion and transition diffusion due to the nanoporous features of OM. Although a single diffusion mechanism in OM has been well-studied, the coexistence of multiple diffusion mechanisms remains unclear. In this work, a local diffusivity lattice Boltzmann model is proposed to consider multiple diffusion mechanisms at the pore-scale. Algorithms of pore network and random-placing sphere are integrated to reconstruct the nanoporous structures of OM. A local Knudsen number is involved to automatically identify local diffusion mechanisms, thus determining the corresponding local diffusivity. The diffusion properties of shale gas in OM are investigated at various shale reservoir pressures and temperatures and OM structural parameters. OM diffusivity is overestimated in the typical pressure range if multiple diffusion mechanisms are ignored. Furthermore, the OM diffusion mechanism gradually transfers from Knudsen diffusion to molecular diffusion with continuously increased pressure. To conveniently predict the diffusion capability of OM, a general empirical formula, which is mainly expressed as a function of porosity and average Knudsen number, is established on the basis of the present simulation results.

MOF-derived N-doped nanoporous carbon framework embedded with Pt NPs for sensitive monitoring of endogenous dopamine release

A Pt NPs encapsulated hollow N-doped carbon framework was constructed by calcinating sandwich-like zinc imidazole framework (ZIF)-67 in N2 atmosphere, and employed for electrochemical detection of dopamine. The morphology and element distribution of this framework was characterized by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The MOF-derived N-doped nanoporous carbon framework can take advantage of the nanoporous features from carbon structures, while Pt NPs maintained good dispersity during calcination. Furthermore, the relevant electrochemical performances were evaluated by amperometry and differential pulse voltammetry (DPV), and the results confirmed that such a structure will robustly promote the electron conduction and mass transfer of dopamine (DA), allowing the quantitative determination of DA with a wide linear range, a low limit of detection (LOD), a high sensitivity and a good selectivity. Based on these observations, the Pt NPs encapsulated hollow N-doped carbon framework modified glassy carbon electrode (CN@Co/Pt/Co-GCE) was further utilized to monitor the endogenous DA released from C6 cells by extracellular K+ stimulation.

Cr-doped BaSnO3 nanoporous thin films with tunable band gap via a facile colloidal solution route

Cr-doped BaSnO3 (BaSn1-xCrxO3, BSCO-x, x = 0–0.15) thin films with nanoporous structure were deposited on fluorine-doped tin oxide substrates via a colloidal solution route. The BSCO-x films exhibited single cubic perovskite phase and nanoporous feature, with the typical specific surface area of 18.98 m2/g and pore size of 10.75 nm (BSCO-0.15). The lowest band gap of 2.68 eV and a high transparency (above 70% in 500–800 nm) were realized in BSCO-0.15 film. This work paves a way toward perovskites with tunable band gap and nanoporous structures for varied photo and photoelectric devices.

Self-assembled bright luminescent hierarchical materials from a tripodal benzoate antenna and heptadentate Eu(III) and Tb(III) cyclen complexes

The europium heptadentate coordinatively unsaturated (Eu(III)) and the terbium (Tb(III)) 1,4,7,10- tetraazacyclododecane (cyclen) complexes 1 and 2 were used in conjunction with ligand 3 (1,3,5-benzene-trisethynylbenzoate) to form the supramolecular self-assembly structures 4 and 5; this being investigated in both the solid and the solution state. The resulting self-assemblies gave rise to metal centered emission (both in the solid and solution) upon excitation of 3, confirming its role as a sensitizing antenna. Drop-cased examples of ligand 3, and the solid forms of 4 and 5, formed from both organic and mixture of organic-aqueous solutions, were analyzed using Scanning Electron Microscopy, which showed significant changes in morphology; the ligand giving rise to one dimensional structures, while both 4 and 5 formed amorphous materials that were highly dense solid networks containing nanoporous features. The surface area (216 and 119 m2·g–1 for 4 and 5 respectively) and the ability of these porous materials to capture and store gases such as N2 investigated at 77 K. The self-assembly formation was also investigated in diluted solution by monitoring the various photophysical properties of 3–5. This demonstrated that the most stable structures were that consisting of a single antennae 3 and three complexes of 1 or 2 (e.g., 4 and 5) in solution. By monitoring the excited state lifetimes of the Eu(III) and Tb(III) ions in H2O and D2O respectively, we showed that their hydration states (the q-value) changed from ∼2 to 0, upon formation of the assemblies, indicating that the three benzoates of 3 coordinated directly to the each of the three lanthanide centers. Finally we demonstrate that this hierarchically porous materials can be used for the sensing of organic solvents as the emission is highly depended on the solvent environment; the lanthanide emission being quenched in the presence of acetonitrile and THF, but greatly enhanced in the presence of methanol.

Nanoporous structure formation on the surface of Ge by ion beam irradiation

The ion beam induced formation of nanoporous structures on the surface of Ge under controlled conditions of ion dose, flux, and irradiation angle using a focused ion beam was investigated by electron microscopy. The formation of large-scale nanoporous structures on the surface of the Ge specimens with increasing ion dose and increasing flux was observed via nanostructural characterization using scanning electron microscopy and transmission electron microscopy (TEM). Compared with the structure formed under irradiation at 0°, that formed under irradiation at 45° was tilted and large-scale. These results suggest that the number of point defects per unit volume of surface is important for the formation of a nanoporous structure. TEM observations revealed that the nanoporous structural features formed during the initial process were not voids but surface roughness. This mechanism differs from the nanoporous structure formation mechanism of GaSb and InSb. The growth of the nanoporous structure in the vertical direction was promoted until the ion dose was 1 × 1021 ions/m2 or greater. At ion doses greater than 1 × 1021 ions/m2, the growth was saturated. The wall thickness remained almost constant with increasing ion dose.

Improving thermal stability of nanoporous platinum cathode at platinum/yttria-stabilized zirconia interface by oxygen plasma treatment

A short oxygen plasma treatment applied on yttria-stabilized zirconia (YSZ) electrolyte of a solid oxide fuel cell has effectively improved the adhesion between the nanoporous Pt thin film cathode and the YSZ electrolyte, which stabilizes the electrochemically active nanoscale features of Pt at YSZ contact interface. After operating at 450 °C for 10 h, the cell with YSZ surface treated by oxygen plasma has retained 88.2% of the fuel cell current output, and the increase of Rohm is approximately 20% lower in the cell with YSZ than the non-treated YSZ. This is because the ion incorporation reaction sites which usually occurs at Pt/YSZ interface is retained by the preservation of nanoporous Pt features at YSZ contact interface.

EBL-Based Fabrication and Different Modeling Approaches for Nanoporous Gold Nanodisks

We report electron beam lithography (EBL) based fabrication and different modeling techniques for disk-shaped nanoporous gold nanoparticles (NPG disk). The EBL technique can provide large area 2D patterns of regularly or randomly distributed nanodisks with narrow size distribution and flexible interdisk (center to center) distance. Such flexibility is essential to obtain quasi-single NPG disk response, which typically peaks in the near-infrared (NIR) spectrum beyond 1 μm, from ensemble measurements by common UV/vis/NIR spectrometers instead of a specialized NIR spectroscopic microscope. NPG disks of 200 to 500 nm diameter and 50 nm thickness have been fabricated and characterized. To model the NPG disk and calculate its plasmonic properties, two different modeling approaches have been developed. A model based on the Bruggeman effective medium theory (B-EMT model) requires little information about the nanoporous structure. In contrast, the nanoporous model (NP model) retains the essential nanoporous structural features of NPG disk. To evaluate the performance of these models, simulated extinction spectra have been compared to the experimental data. Both the B-EMT and NP models perform well to estimate the far-field plasmon resonance peak position. However, to obtain the accurate information about the plasmon peak width/plasmon lifetime and near-field plasmonic hot-spots formation within the nanopores, the NP model is essential since the B-EMT model lacks the nanoporous network.

Nanoporous Structure Formation in GaSb, InSb, and Ge by Ion Beam Irradiation under Controlled Point Defect Creation Conditions.

Ion beam irradiation-induced nanoporous structure formation was investigated on GaSb, InSb, and Ge surfaces via controlled point defect creation using a focused ion beam (FIB). ‎This paper compares the nanoporous structure formation under the same extent of point defect creation while changing the accelerating voltage and ion dose. Although the same number of point defects were created in each case, different structures were formed on the different surfaces. The depth direction density of the point defects was an important factor in this trend. The number of point defects required for nanoporous structure formation was 4 × 1022 vacancies/m2 at a depth of 18 nm under the surface, based on a comparison of similar nanoporous structure features in GaSb. The nanoporous structure formation by ion beam irradiation on GaSb, InSb, and Ge surfaces was controlled by the number and areal distribution of the created point defects.

Rational Design of Branched Nanoporous Gold Nanoshells with Enhanced Physico-Optical Properties for Optical Imaging and Cancer Therapy.

Reported procedures on the synthesis of gold nanoshells with smooth surfaces have merely demonstrated efficient control of shell thickness and particle size, yet no branch and nanoporous features on the nanoshell have been implemented to date. Herein, we demonstrate the ability to control the roughness and nanoscale porosity of gold nanoshells by using redox-active polymer poly(vinylphenol)-b-(styrene) nanoparticles as reducing agent and template. The porosity and size of the branches on this branched nanoporous gold nanoshell (BAuNSP) material can be facilely adjusted by control of the reaction speed or the reaction time between the redox-active polymer nanoparticles and gold ions (Au3+). Due to the strong reduction ability of the redox-active polymer, the yield of BAuNSP was virtually 100%. By taking advantage of the sharp branches and nanoporous features, BAuNSP exhibited greatly enhanced physico-optical properties, including photothermal effect, surface-enhanced Raman scattering (SERS), and photoacoustic (PA) signals. The photothermal conversion efficiency can reach as high as 75.5%, which is greater than most gold nanocrystals. Furthermore, the nanoporous nature of the shells allows for effective drug loading and controlled drug release. The thermoresponsive polymer coated on the BAuNSP surface serves as a gate keeper, governing the drug release behavior through photothermal heating. Positron emission tomography imaging demonstrated a high passive tumor accumulation of 64Cu-labeled BAuNSP. The strong SERS signal generated by the SERS-active BAuNSP in vivo, accompanied by enhanced PA signals in the tumor region, provide significant tumor information, including size, morphology, position, and boundaries between tumor and healthy tissues. In vivo tumor therapy experiments demonstrated a highly synergistic chemo-photothermal therapy effect of drug-loaded BAuNSPs, guided by three modes of optical imaging.