Nanoparticle-induced drag reduction for polyacrylamide in turbulent flow with high Reynolds numbers

Although having been increasingly studied, there is still controversy as to when the addition of nanoparticles could improve the drag reduction performance of polymer drag reducer and particularly what is the underlying mechanism from the fluid dynamics viewpoint. The drag reduction effects of adding SiO_(2) nanoparticles to various polymer polyacrylamide(PAM) solutions were examined in this work.The optimal combination of SiO_(2) nanoparticles with cationic polyacrylamide was confirmed.Interestingly,the addition of SiO_(2) nanoparticles to cationic polyacrylamide solution was shown to be quite efficient for reducing drag, but only at higher flow rates with Reynolds numbers more than 6000, below which the nanoparticle addition is even negative. The addition of SiO_(2) nanoparticles to the PAM solution is supposed to play a dual role. The first is an increase in flow resistance caused by the Brownian motion of nanoparticles, while the second is a decrease in flow resistance caused by acting as nodes to protect the polymer chain from shear-induced breaking under high shear action. At optimal nanoparticle concentration and under higher Reynolds numbers, the later effect is dominant, which could improve the drag reduction performance of polymer drag reducers. Our work should serve as a guide for the application of natural gas fracturing, where the flow rate is frequently very high.

MgO and Au nanoparticle Co-modified g-C_(3)N_(4)photocatalysts for enhanced photoreduction of CO_(2)with H_(2)O

The photoreduction of CO_(2)to achieve high-value-added hydrocarbons under simulated sunlight irradiation is advantageous,but challenging.In this study,a series of MgO and Au nanoparticle-co-modified g-C_(3)N_(4)photocatalysts were synthesized and subsequently applied for the photocatalytic reduction of CO_(2)with H2O under simulated solar irradiation.The best photocatalytic performance was demonstrated by the Au and 3%MgO-co-modified g-C_(3)N_(4)photocatalysts with CO,CH_(4),CH3OH,and CH3CHO yields of 423.9,83.2,47.2,and 130.4μmol/g,respectively,in a 3-h reaction.We investigated the effects of MgO and Au as cocatalysts on photocatalytic behaviors,respectively.The characterizations and experimental results showed that the enhanced photocatalytic activity was due to the synergistic effect among the components of the ternary photocatalyst.The cocatalyst MgO can activate CO_(2)(adsorbed at the interface between the MgO and Au particles),and the Mg-N bonds formed in the MgO-CN nanosheets played an important role in the charge transfer.Meanwhile,the Au particles that were modified into MgO/g-C_(3)N_(4)can increase the absorption of visible light via the surface plasmon resonance effect and further reduce the activation energies of the photoreduction of CO_(2)using H2O.This study provided an effective method for the modification of traditional primary photocatalysts with promising performance for photocatalytic CO_(2)reduction.

Hydrodynamic and heat transfer properties of magnetic fluid in porous medium considering nanoparticle shapes and magnetic field-dependent viscosity

The purpose of this paper is to study the characteristics of the combined convection heat transfer and a micropolar nanofluid flow passing through an impermeable stretching sheet in a porous medium.The nanofluid flow field is affected by a magnetic field perpendicular to the sheet.The dynamic viscosity of the micropolar nanofluid changes under the influence of the magnetic field.The continuity,linear momentum,angular momentum,and energy equations are first simplified using the order of magnitude technique that,along with the applied boundary conditions and the definition of the appropriate parameters,are transferred to the similarity space using the similarity analysis.Then the resulting equations are solved using the Runge–Kutta method.The distinction of the macroscale and microscale flow fields and temperature fields resulting from different nanoparticle shapes was clarified.Increasing the Hartmann number,the vortex viscosity parameter,the magnetic parameter,the nanoparticle volume fraction,and the permeability parameter of the porous media increased the surface friction on the sheet.Increasing the vortex viscosity parameter,the magnetic parameter,and the volume fraction of the nanoparticles increases the Nusselt number.

Enhanced efficiency in Concentrated Parabolic Solar Collector(CPSC) with a porous absorber tube filled with metal nanoparticle suspension

In this study, effects of different nanoparticles and porosity of absorber tube on the performance of a Concentrating Parabolic Solar Collector(CPSC) were investigated. A section of porous-filled absorber tube was modeled as a semi-circular cavity under the solar radiation which is filled by nanofluids and the governing equations were solved by FlexPDE numerical software. The effect of four physical parameters, nanoparticles type, nanoparticles volume fraction(φ), Darcy number(Da) and Rayleigh number(Ra), on the Nusselt number(Nu) was discussed. It turns out that Cu nanoparticle is the most suitable one for such solar collectors, compared to the commonly used Fe_3O_4, Al_2O_3, TiO_2.With the increased addition of Cu nanoparticles all the parameters φ, Da and Ra shows a significant increase against the Nu, indicates the enhanced heat transfer in such cases. As a result, low concentration of Cu nanoparticle suspension combined with porous matrix was supposed to be beneficial for the performance enhancement of concentrating parabolic solar collector.

Boosting photocatalytic hydrogen production via interfacial engineering over a Z-scheme core/shell heterojunction

Designing high efficacy photocatalysts is a promising way to improve solar fuel production efficiency.In this work,we prepared a core/shell composite of loose ZnCr layered double hydroxide nanosheets modified CdS nanorods for efficient visible light driven photocatalytic hydrogen production.The highest hydrogen production rate achieved 425.8μmol·h^(−1) without adding any noble metal cocatalyst under the visible light stimulus,which is 22.4 times that of 1 wt.%Pt-modified CdS.The corresponding apparent quantum yield is 13.9%at 420 nm.It is revealed that the synergistic actions of the interfacial redox shuttle of Cr^(3+)/Cr^(δ+)and the interfacial electric field enable the efficient separation of photoinduced charge carriers between two components via a Z-scheme energy band configuration.Meanwhile,with the hydrogen evolution contribution of Zn^(2+),a remarkable improvement in photocatalytic performance was achieved in contrast to bare CdS.This work provides an effective methodology to construct highly efficient and economically viable photocatalysts for solar H_(2)production and mechanistic study.

Enhanced photodynamic therapy of mixed phase TiO2（B）/anatase nanofibers for killing of HeLa cells

Photodynamic therapy （PDT）, which is a procedure that uses photosensitizing drug to apply therapy selectively to target sites, has been proven to be a safe treatment for cancers and conditions that may develop into cancers. Nano-sized TiO2 has been regarded as potential photosensitizer for UV light driven PDT. In this study, four types of TiO2 nanofibers were prepared from proton tri-titanate （H2T3O7） nanofiber. The as-obtained nanofibers were demonstrated as efficient photosensitizers for PDT killing of HeLa cells. MTT assay and flow cytometry （FCM） were carried out to evaluate the biocompatibility, percentage of apoptotic cells, and cell viability. The non-cytotoxicity of the as-prepared TiO2 nanofibers in the absence of UV irradiation has also been demonstrated. Under UV light irradiation, the TiO2 nanofibers, particularly the mixed phase nanofibers, displayed much higher cell-killing efficiency than Pirarubicin （THP）, which is a common drug to induce the apoptosis of HeLa cells. We ascribe the high cell- killing efficiency of the mixed phase nanofibers to the bandgap edge match and stable interface between TiO2（B） and anatase phases in a single nanofiber, which can inhibit the recombination of the photogenerated electrons and holes. This promotes the charge separation and transfer processes and can produce more reactive oxygen species （ROS） that are responsible for the killing of HeLa cells.

Noble-metal free plasmonic nanomaterials for enhanced photocatalytic applications—A review

Plasmonic nanomaterial catalysis is currently at the frontier of photocatalysis,overcoming the limitations of wide bandgap semiconductors for light absorption.Its localized surface plasmon resonance(LSPR)properties allow broad ultraviolet-visible-near infrared ray(UV-vis-NIR)absorption,making it an ideal material for solar energy conversion.Most plasmonic nanostructures rely on precious metals.Although noble metal plasmonic nanomaterials have proven to be one of the strategies for enhancing photocatalytic activity,their expensive cost and limitations in light absorption range have hindered their practical application.As a result,noble-metal free plasmonic nanomaterials have risen to the top of the research priority list.Therefore,this paper reviews the fundamental principles and classification of the LSPR effect of noble-metal free plasmonic nanomaterials in photocatalytic and their recent applications in hydrogen generation,carbon dioxide reduction,and pollutant degradation.Specific cases elucidate the possible working mechanism of enhanced photocatalysis by noble-metal free plasmonic nanomaterials.Finally,the challenges and future opportunities for noble-metal free plasmonic nanomaterials in energy conversion and storage are discussed and envisioned.

Solar photocatalytic energy conversion

Development of clean and renewable energy sources is an inevitable choice of human society to address the energy shortage and environmental deterioration problems nowadays.Hydrogen has been recognized as the most ideal and clean fuel because its burning product is water without second pollution.Hydrogen is

State-of-the-art progress in overall water splitting of carbon nitride based photocatalysts

Converting solar energy into hydrogen(H_(2))by photocatalytic water splitting is a promising approach to simultaneously address the increasing energy demand and environmental issues.Half decade has passed since the discovery of photo-induced water splitting phenomenon on TiO_(2)photoanode,while the solar to H_(2) efficiency is still around 1%,far below the least industrial requirement.Therefore,developing efficient photocatalyst with a high energy conversion efficiency is still one of the main tasks to be overcome.Graphitic carbon nitride(g-C_(3)N_(4))is just such an emerging and potential semiconductor.Therefore,in this review,the state-of-the-art advances in g-C_(3)N_(4)based photocatalysts for overall water splitting were summarized in three sections according to the strategies used,and future challenges and new directions were discussed.

Theoretical study on flow and radiation in tubular solar photocatalytic reactor

In this paper,based on the mixture flow model,an optimized six-flux model is first established and applied to the tubular solar photocatalytic reactor.Parameters influencing photocatalyst distribution and radiation distribution at the reactor outlet,viz.catalyst concentration and circulation speed,are also analyzed.It is found that,at the outlet of the reactor,the optimized six-flux model has better performances(the energy increase by 1900%and 284%,respectively)with a higher catalyst concentration(triple)and a lower speed(one third).

Evaporation and drying characteristics of the sessile ferrofluid droplet under a horizontal magnetic field

In this study,the evaporation characteristics and drying patterns of various sessile ferrofluid droplets on certain substrate under horizontal magnetic fields of controlled intensities are reported.The effects of droplet concentration and magnetic field intensity on the duration of each evaporation stage and drying patterns of droplets have been systematically investigated.It turned out that a plateau appears at the initial stage of evaporation in the absence of magnetic field and it was found that the plateau value is positively correlated with the concentration of ferrofluid droplets.Under the external magnetic field,the evaporation time of droplets decreases,the stage of contact line retreat extends,the stage of late pinning mode shortens,and the deposition area of ferrofluid droplet decreases compared to that of without magnetics field.The deposition area increases gradually and becomes more uniform with the increase of magnetic field.The decrease of friction force which is due to the decrease of the number of nanoparticles at the contact line under external magnetic field is the main reason for the observed phenomena.We found that the coffee ring and the uniform deposition inside the droplet will be destroyed when the magnetic field intensity is higher than a critical value.Our work has a significant reference value for the evaporation of sessile magnetic fluid droplets under the applied magnetic field,especially when the drying pattern needs to be precisely controlled,such as in spray or biomedicine.