From ultra-low friction to superlubricity state of black phosphorus:Enabled by the critical oxidation and load

Based on the density functional theory(DFT),we investigate the friction properties of inevitable oxidized black phosphorus(o-BP).o-BP with the weaker interlayer adhesion exhibits their great potential as a solid lubricant.At the zero load,the friction property of o-BP is adjusted by its oxidation degree.Expressly,ultra-low friction of P4O2(50%oxidation,O:P=2:4=50%)is obtained,which is attributed to the upper O atoms with lower sliding resistance in the O channel formed by lower layer O atoms.More attractive,we observe superlubricity behavior of o-BP at the critical load/distance due to the flattening potential energy surface(PES).The flattening PES is controlled by the electrostatic role for the high-load(P4O3,O:P=3:4=75%),and by the electrostatic and dispersion roles for the low-load(P4O2).Distinctly,the transform from ultra-low friction to superlubricity state of black phosphorus(BP)can be achieved by critical oxidation and load,which shows an important significance in engineering application.In addition,negative friction behavior of o-BP is a general phenomenon(Z>Z_(min),Z_(min)is the interlayer distances between the outermost P atoms of minimum load.),while its surface-surface model is different from the fold mechanism of the tip-surface model(Z_(0)<Z<Z_(min),Z_(0)is the interlayer distances between the outermost P atoms of equilibrium state.).Thus,this phenomenon cannot be captured due to the jump effect with instability of the atomic force microscopy(AFM)(Z>Z_(min)).In summary,o-BP improves the friction performance and reduces the application limitation,comparing to graphene(Gr),MoS2,and their oxides.

Heterogeneous oxidation of SO_2 by O_3-aged black carbon and its dithiothreitol oxidative potential

Ozone（O3） is an important atmospheric oxidant. Black carbon（BC） particles released into the atmosphere undergo an aging process via O3 oxidation. O3-aged BC particles may change their uptake ability toward trace reducing gases such as SO2 in the atmosphere,leading to different environmental and health effects. In this paper, the heterogeneous reaction process between O3-aged BC and SO2 was explored via in-situ diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）. Combined with ion chromatography（IC）,DRIFTS was used to qualitatively and quantitatively analyze the sulfate product. The results showed that O3-aged BC had stronger SO2 oxidation ability than fresh BC, and the reactive species/sites generated on the surface had an important role in the oxidation of SO2.Relative humidity or 254 nm UV（ultraviolet） light illumination enhanced the oxidation uptake of SO2 on O3-aged BC. The oxidation potentials of the BC particles were detected via dithiothreitol（DTT） assay. The DTT activity over BC was decreased in the process of SO2 reduction, with the consumption of oxidative active sites.

Black tantalic oxide submicro-particles coating on PEEK fibers woven into fabrics as artificial ligaments with photothermal antibacterial effect and osteogenic activity for promoting ligament-bone healing

Design of artificial ligaments possessing both osteogenic activity and antibacterial effect that promotes ligament-bone healing and prevents bacterial infection in bone tunnels for anterior cruciate ligament(ACL)reconstruction remains a significant challenge.In this study,black tantalic oxide(BTO)submicro-particles with oxygen vacancies and structure defects were fabricated by using traditional white tan-talic oxide(WTO)through magnesium thermal reduction(MTR)method,and BTO was coated on polyetheretherketone(PEEK)fibers(PKF),which were woven into fabrics(PBT)as artificial ligaments.PBT with BTO coating exhibited excellent photothermal performance,which possessed not only antibac-terial effects in vitro but also anti-infective ability in vivo.PBT with optimized surface properties(e.g.,submicro-topography and hydrophilicity)not only significantly facilitated rat bone mesenchymal stem cells(BMSC)responses(e.g.,proliferation and osteogenic differentiation)in vitro but also stimulated new bone formation for ligament-bone healing in vivo.The presence of oxygen vacancies and structure de-fects in BTO did not change the surface properties and osteogenic activity of BPT while displaying an outstanding photothermal antibacterial effect.In summary,BPT with osteogenic activity and photother-mal antibacterial effect promoted bone regeneration and prevented bacterial infection,thereby promoting ligament-bone healing.Therefore,PBT would have tremendous potential as a novel artificial ligament for ACL reconstruction.

Ultrafast nonlinear absorption and nonlinear refraction in few-layer oxidized black phosphorus

We experimentally investigated the nonlinear optical response in few-layer oxidized black phosphorus(OBP) by the femtosecond Z-scan measurement technique, and found that OBP not only possesses strong ultrafast saturable absorption but also a nonlinear self-defocusing effect that is absent in black phosphorus(BP). The saturable absorption property originates mainly from the direct band structure, which is still maintained in OBP. The emergence of self-defocusing might originate from the combined consequences of the oxygen-induced defects in BP. Our experimental findings might constitute the first experimental evidence on how to dynamically tune its nonlinear property, offering an inroad in tailoring its optical properties through chemical modification(oxidation, introducing defects, etc.). The versatile ultrafast nonlinear optical properties(saturable absorption and self-defocusing) imply a significant potential of the layered OBP in the development of unprecedented optoelectronic devices, such as mode lockers, optical switches, laser beam shapers, and wavelength converters.

Oxidized Black Phosphorus Nanosheets as an Inorganic Antiresorptive Agent

Black phosphorus(BP)is a newly discovered two-dimensional material that has promising applications from bioelectronics to biomedicine.However,facile oxidation of BP leads to changes in surface chemical composition and physical properties,often being referred to as the degradation process of BP.Degradation products of BP nanosheets,namely,oxidized BP nanosheets(oBPNSs),are routinely considered as by-products without many uses.Herein,we found that oBPNSs displayed excellent osteoclastogenesis inhibition effects without impairing cell viability.In contrast to the classic antiresorptive bisphosphonate drugs,oBPNSs showed a different mode of action by suppressing the maturation of osteoclasts.Bone resorption assays,osteoclast actin ring analysis,and tartrate-resistant acid phosphate activity assay results indicated that oBPNSs suppressed receptor activator of nuclear factor-κB(NF-κB)ligand(RANKL)-induced osteoclastogenesis in a dose-and oxidation-dependent manner.Transcriptomic and proteomic analyses indicated that oBPNSs inhibited the activation of the NF-κB signaling pathway and phosphorylation of mitogen-activated protein kinase(MAPK)in differentiated osteoclasts,as confirmed by Western blot analysis.Our results suggest that oBPNSs might be potential antiresorptive nanomaterials to treat osteoporosis.