Open Access
Issue
Natl Sci Open
Volume 3, Number 5, 2024
Article Number 20230073
Number of page(s) 14
Section Chemistry
DOI https://doi.org/10.1360/nso/20230073
Published online 25 April 2024

© The Author(s) 2024. Published by Science Press and EDP Sciences.

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

INTRODUCTION

Nanomaterials have been extensively studied and applied to biomedicine [13]. Black phosphorus (BP), as a biofriendly material, is considered as a promising vehicle for anticancer drugs due to its favorable biocompatibility, strong photothermal effect, high drug loading capacity, and bioimaging capabilities [47]. As a kind of biomedical carrier, BP has been widely concerned and studied for its migration process in vivo and its stability behavior. Since BP nanosheets are linked together by monolayers of BP under van der Waals interactions, leading to their instability [8]. Currently, many studies have shown the oxidation of BP occurs in the natural environment and organisms [9,10]. At present, many studies have found that oxygen, water and light [1113] are the main influencing factors in the oxidation of BP. Phosphate, phosphite, and hypophosphite are the major oxidation products [1416].

Phosphate, as the oxidation product of BP, has been utilized in the treatment of bone defects [17,18] and in the induction of autophagy and apoptosis in cancer cells [19]. Nevertheless, the low yield of phosphate molecules has hindered the utilization of BP.

In addition, when BP migrates in organisms, it will contact with a variety of metal ions, such as the major metal elements sodium, magnesium, calcium and trace metal elements copper, iron and manganese [20]. However, the stability behavior of BP in contact with these metal ions is not well understood, which will make its migration and transformation behavior more complex. At present, relevant studies have found that the surface chemistry of BP will be changed when it contacts with metal, which will further affect its stability. For example, copper ions (Cu2+) can specifically adsorb on the surface of BP [21], while silver ions (Ag+) can bind BP through cation-Π, which enhances the stability of BP in the environment [22], which will increase its residence time and potential risk [23]. Therefore, it is necessary to investigate the stability of BP with the presence of metal ions.

Therefore, eight common metal ions in living organisms were selected in this study to investigate the stability behavior of BP in the presence of metal ions. Furthermore, Cu2+ was found to accelerate the oxidation of BP and enhance phosphate yield. A variety of characterization techniques and density functional theory (DFT) calculations were combined to explain the role of Cu2+ in the reaction.

This study offers a novel perspective on the oxidation behavior of BP and proposes a new approach to increase the yield of phosphate. Furthermore, it contributes to the advancement of the practical application of BP.

RESULTS

Characterization of Few-layered BP

The mass concentration of BP in water was measured by ultraviolet-visible (UV-vis) spectroscopy and the standard curve was displayed in Figure S1. Transmission electron microscopy (TEM) was used to characterize the morphology of the prepared BP, and it was found that the few-layered BP presented a sheet-like morphology (Figure 1a), similar to previous studies [16]. High-resolution TEM (HRTEM) image showed that the lattice spacing correlated well with 0.26 nm (Figure 1b), indicating the presence of crystalline BP, consistent with the results reported in previous studies [24]. The selective area electron diffraction (SAED) pattern of BP presented in the inset image of Figure 1b further confirmed the perfect crystalline of BP. These results demonstrated that the crystallinity of the material remained intact after being subjected to a mechanical exfoliation process in an ambient environment. Three typical bands corresponding to A1g, B2g, and A2g of BP at 363.1, 437.3 and 468.1 cm−1 were observed in the Raman spectrum, respectively (Figure 1c) [25]. The lateral size and thickness of few-layered BP were determined to be 200–1000 nm and ~1.8 nm based on the analysis of the atomic force microscopy (AFM) images (Figure 1d–f).

thumbnail Figure 1

Characterization of the prepared BP. (a) TEM image of few-layered BP. (b) HRTEM image of BP. The inset image showed the corresponding SAED pattern. (c) Raman spectrum of BP. (d) AFM image of BP. (e) The height profiles of BP along the white lines in (c). (f) Histogram of BP size distribution. The histograms were developed by counting 200 sheets for each sample, with Gaussian fit curves shown in each histogram.

Cu2+ accelerated the oxidation of BP

BP has a negative surface charge and can bind to a variety of metal ions. Consequently, the main metal elements such as sodium (Na+ ), magnesium (Mg2+ ), and calcium (Ca2+ ) and trace metals such as copper (Cu2+ ), iron (Fe3+ ), manganese (Mn2+), zinc (Zn2+), and cobalt (Co2+) in human body were selected to bind with BP, and their effects on the stability of BP were studied. Figure 2a showed that 90% of BP was removed within 12 h in the presence of Cu2+. In comparison, about 10%–20% of BP was oxidated in the presence of Mn2+, Mg2+, Ca2+, Zn2+, Co2+, Na+ or Fe3+ in the reaction system, respectively. These findings suggest that the presence of Cu2+ significantly enhanced the oxidation of BP. The effect of Cu2+ concentrations on the oxidation rate of BP over time was further investigated. As shown in Figure 2b, the oxidation rate of BP increased with the increase of Cu2+ concentration. The removal of BP followed the first-order decay (C = C0ekt) at the tested Cu2+ concentrations (Figure 2c). The pseudo-first-order kinetic constants were calculated according to fitted lines for various concentrations, which were plotted in Figure 2d. The well fitted linear regression model suggested that the oxidation of BP mediated by Cu2+ could be described using the second-order reaction kinetics. The second order rate constant of reaction was 0.00432 L h/μmol. The oxidation rates of BP under different concentrations (Figure S2) were also investigated.

thumbnail Figure 2

(a) Oxidation of BP over time with different kinds of metal ions. (b) Oxidation rates of BP at different Cu2+ concentrations. (c) Pseudo-first-order rate plots for oxidation of BP. (d) Relationship between pseudo-first-order rate constants and Cu2+ concentration. (b–d) Experimental conditions were as follows: the absorbance of BP was 0.5, [Cu2+] = 1–20 μmol/L, pH = 7.0, 25°C. Error bars represent standard deviations (n = 3).

Temperature will affect the rate of the reaction, while pH will change the zeta potential of the metal ion solution. The effects of temperature and pH on the reaction system were evaluated at different conditions, namely kept at 4, 25, 40 and 60°C, and maintaining a pH range of 3, 5, 7, 9, and 11 using an acid-base buffer solution (Figure S3). The results demonstrated that high temperatures accelerated the oxidation rate of BP, while the influence of solution pH on the reaction of BP mediated by Cu2+ was insignificant. In this experiment, only the effect of bare metal ions on the stability of BP was investigated, while metal ions are mostly wrapped by proteins in organisms. Therefore, ethylene diamine tetraacetic acid-Cu (EDTA-Cu) and laccase (a Cu-rich protease) [26] were chosen to explore the effect of Cu2+ on BP in organisms and it was found that both of them can enhance the oxidation of BP (Figure S4). However, the effect of real proteins on the stability of BP and the effect of protein crowns on BP encapsulation need to be further explored [27].

Reaction products of BP

Reaction products of BP were identified in the reaction with and without the presence of Cu2+, respectively. Raman spectroscopy was employed to characterize the structure changes of BP at different reaction times. The reliable Ag1/Ag2 ratio was used to assess the extent of BP oxidation [28]. After 2 h of reaction, the Ag1/Ag2 ratios decreased from 0.62 to 0.48, as observed in Figure 3a, providing evidence for the oxidation of BP in the presence of Cu2+. The three characteristic peaks of BP, Ag1, B2g, and Ag2, all showed a significant decrease of 46%, 31%, and 35%, respectively. To determine the chemical composition of the BP surface, P 2p spectra of the pristine BP and BP oxidized with Cu2+ for 2 h were obtained. As presented in Figure 3b, BP exhibited 2p3/2 and 2p1/2 peaks at 130.1 and 131.0 eV, respectively [29,30], which were similar to bulk BP 2p peak positions, suggesting that the structure of most BP did not undergo great change during the two-hour oxidation process. The peak at 134 eV, however, showed a substantial increase, indicating the formation of PxOy on the BP surface resulting from oxidation. TEM characterization revealed that during the oxidation process, the edges of BP became round, as shown in Figure 3c and d, and black spots were found to be attached, confirmed through energy dispersive spectrometer (EDS) analysis as copper element. In-situ AFM characterization was also carried out to explore the specific location of BP oxidation. The AFM measurements demonstrated that, initially, BP had an irregular edge with a thickness of approximately 4.0 nm. After the addition of Cu2+ for 10 min, the two ends of BP disappeared, indicating that part of BP was oxidized to PxOy and desorbed into the solution. The thickness of BP at the same position varied to approximately 4.2 nm due to the formation of PxOy adsorbed on the surface of BP. After 1 h of reaction, more parts of BP at two ends disappeared, and the edge became smooth and round. Additionally, the thickness of BP changed from approximately 4.2 nm to approximately 3.7 nm, signifying that PxOy also desorbed into the solution continuously. In the three-dimensional (3D) image (Figure S5), areas of increased thickness at the edge of BP were observed, corresponding to the bright spot in the 2D image, which may be interpreted as a signal of oxidation and desorption. Based on the aforementioned observations, we hypothesized that both the edge and the surface of BP were oxidized at the same time for Cu2+ adsorbed uniformly by BP. However, the desorption rate at the edge was obviously faster than that at the surface, which may be caused by the larger contact area of the edge with the solution.

thumbnail Figure 3

Characterization of BP during the reaction. (a) Raman spectra of BP in 20 μmol/L Cu2+ solution at 0 and 2 h. (b) XPS spectra of BP exposed to Cu2+. The morphology of the BP sheet at 0 h (c) and 2 h (d) after reaction with Cu2+. The white tip indicates the complete edge of the BP sheet. The yellow tip indicates the rounded edge after partial oxidation, and the red circle indicates the black spots loaded on the surface of BP. (e) In situ AFM images acquired with Cu2+ at different times, showing the morphology evolution of a BP sheet. (f) Height profiles of the BP nanoflake acquired along the dashed lines in panel (e).

Ion chromatography was used to identify the oxidation products of BP and three kinds of oxidation products of BP were found, namely phosphate (PO43−), phosphorous (PO33−), and hypophosphite (PO23−). The standard curves for the three products are shown in Figure S6. Figure 4a showed that the concentration of PO43−, PO33−, and PO23− increased by 112.2, 102.3, and 39.2 μmol/L, respectively, within 15 d. Figure 4b showed the mole fractions of PO43− (~45 mol%), PO33− (~40 mol%) and PO23− (~15 mol%) in water were almost unchanged, which is consistent with Zhang’s results [16]. Figure 4c showed that the concentrations of PO33− and PO23− had no significant change, while that of PO43− increased significantly. At 24 h, the concentrations of PO43−, PO33−, and PO23− were 223.3, 25.5, and 12.6 μmol/L, respectively. Figure 4d illustrated that >85% of the reaction products were PO43− for the reaction of BP with Cu2+. The fraction alteration of the oxidation products of BP revealed that the participation of Cu2+ changed the reaction pathway.

thumbnail Figure 4

Relative concentrations of PO43−, PO33− and PO23− compared to the values at the initial state measured by IC in the absence of Cu2+ (a) and in the presence of Cu2+ (c). Mole fractions of PO43−, PO33−, and PO23− were measured at different storage times in the absence of Cu2+ (b) and in the presence of Cu2+ (d).

Reaction pathway and possible mechanisms

The oxidation process of BP in air is predominantly controlled by the presence of oxygen, water, and light [1113], thus the impact of each of these components on the BP-Cu2+ reaction system was examined. Our experimental findings suggest that, while light had a negligible effect on the reaction system, water and oxygen were indispensable components of the reaction, as demonstrated in Figure S7. At the same time, reactive oxygen species are considered to be important factors affecting the oxidation of BP [31]. Therefore, quenching agents including hydroxyl radical, singlet oxygen and superoxide anion are selected to evaluate the possible participation of reactive oxygen in the reaction. As shown in Figure S8, the effect of reactive oxygen species is almost negligible in the current experiment.

Drawing upon the aforementioned results and available literature on Cu2+ as mediators, we postulated that the BP-Cu2+ reaction system can be conceptualized to comprise three distinct processes (Figure 5): (i) the enhanced adsorption and bonding of oxygen to the BP-Cu2+ surface, triggered by the presence of Cu2+; (ii) the oxidation of the BP surface layer into three kinds of phosphate groups and the simultaneous reduction of Cu2+ to cuprous ions; (iii) the release of the phosphate groups into the solution and the subsequent dissolution of cuprous ions from the BP surface. While the above three steps are carried out, the shed cuprous ions are oxidized to Cu2+ by the ambient oxygen, and continue to participate in the reaction.

thumbnail Figure 5

The mechanism of rapid oxidation of BP in the presence of Cu2+.

In step I, Cu2+ was quickly adsorbed onto the BP surface at first, and then oxygen molecules were adsorbed between Cu2+ and BP to form chemical bonds. To corroborate the hypothesis of rapid Cu2+ adsorption onto the BP surface, a series of adsorption experiments involving various ions on the BP surface were conducted. As depicted in Figure 6a, nearly all of the added Cu2+ were rapidly absorbed by the BP, while the adsorption capacity of the BP for iron ions was limited to approximately 50%, which was consistent with the adsorption results in other studies [21]. The adsorption rate of various other tested metal ions was also markedly lower than that of Cu2+, thereby corroborating the promotion performance of BP observed in Figure 2A. Moreover, to determine the adsorption time of Cu2+ on BP, experiments were conducted for varying adsorption periods. In order to explore the adsorption time between BP and Cu2+, adsorption experiments were performed at different time points. Figure 6b manifested that Cu2+ was adsorbed within 1 min on the BP surface. Nevertheless, a more meticulous investigation is warranted to discern the precise adsorption time between BP and Cu2+.

thumbnail Figure 6

(a) Bind capacity of BP nanosheets to different metal ions. (b) Adsorption kinetics curve of BP on the Cu2+. (c) XPS spectra of BP nanosheets before and after Cu adsorption for 1 h. (d) Schematic diagram of oxygen molecule adsorption on the surface of BP before and after Cu adsorption.

To verify that Cu2+ could enhance the adsorption capacity of BP to oxygen molecules, X-ray photoelectron (XPS) and DFT calculations were performed. The XPS spectra revealed the emergence of a new peak in the range from 122 to 124 eV in the BP-Cu2+ group that was absent in the control group (Figure 6c). Preliminary inspection by the National Institute of Standards and Technology (NIST) suggested that this peak may be linked to the P–Cu–O bond, a finding not previously reported in the literature. To further validate this observation, DFT calculations were conducted to gauge the energy required for oxygen adsorption on the BP surface, with or without the presence of Cu2+. As depicted in Figure 6d, the energy required for oxygen molecule adsorption onto the pure BP surface was −0.27 eV, while this value plummeted to −2.33 eV in the presence of Cu2+. Moreover, upon the addition of another oxygen molecule to the model, the binding was still intact, and the required energy (−2.1 eV) remained considerably lower than that observed without the intervention of Cu2+. Similar DFT calculations (Figure S9) performed at the BP edge equally supported our hypothesis that Cu2+ facilitated oxygen binding on the BP.

In step II, Cu2+ mediated the oxidation of BP into three distinct phosphoric acid products. There are two widely accepted views on the oxidation of BP without Cu2+. First of all, water molecules are known to pluck the surface oxides of BP in the course of their oxidation, owing to hydrogen bonding [30]. In addition, Zhang’s research [16] identified three distinct oxidation products of BP. However, in contrast to extant studies, the addition of Cu2+ exerted a discernable impact on the formation and desorption energies of these phosphoric acid molecules, leading to modifications in their actual formation ratios. The formation energies of the three phosphoric acid molecules on pure BP and BP-Cu2+ complexes were calculated using DFT. As illustrated in Figure 7a, the formation energies of H3PO2, H3PO3, and H3PO4 on the pure BP surface were computed to be −1.96, −3.81, and −6.89 eV, respectively. By contrast, on the BP-Cu2+ complex surface (Figure 7b), these energy values were found to be −4.62, −7.03, and −9.83 eV, respectively. These calculation results showed that in the presence of Cu2+, the formation energy of the three phosphate molecules decreases, indicating that they were generated faster than before, which leads to a faster oxidation rate of BP. This result was consistent with the results in Figure 2a.

thumbnail Figure 7

(a) Structure of the formed H3POx and the corresponding formation energies for pristine BP. (b) Structure of the formed H3POx and the corresponding formation energies for Cu@BP. (c) Desorption barrier of H3POx from BP calculated by CI-NEB method. (d) Desorption barrier of H3POx from Cu@BP calculated by CI-NEB method.

At the same time, Cu2+ would be reduced to cuprous ions, and XPS was carried out to prove it. Figure S10A showed that Cu2+ mainly existed in the form of copper monovalent. Also, we tried to use monovalent copper ions to accelerate the oxidation of BP, and found that the promoting effect of cuprous ions was the same as that of copper ions (Figure S10B).

In step III, the three kinds of phosphate moieties overcame the adsorption energy barrier and desorbed from the surface of BP. The desorption energies of the three phosphoric acid molecules at both pure BP and BP-Cu2+ complexes were calculated via DFT. As displayed in Figure 7c, the desorption energies of H3PO2, H3PO3, and H3PO4 on pure BP surfaces were 0.93, 0, and 0.66 eV, respectively. While the phosphoric acid molecule exhibited a lower formation energy (−6.89 eV), a desorption energy of 0.66 eV was required. By comparison, the formation energy for the phosphite molecule (−3.81 eV) did not necessitate any additional energy for its detachment, and hence the highest proportion of phosphite was found in the oxidation products of BP, which was consistent with the results of Figure 4b. In the presence of Cu2+, the desorption energies of the three phosphoric acid molecules were increased to 1.39, 1.41, and 1.24 eV, respectively. Thereby, the calculation results showed that the desorption energy of phosphate molecule was the lowest among the three, and its formation energy was the lowest at 9.83 eV, implying that the proportion of phosphate molecule in the oxidation product of BP was the highest, which was consistent with the results in Figure 4d. As the three phosphoric acid molecules detached and were shed from the BP surface, additional defect sites became exposed, thus facilitating subsequent reactions.

CONCLUSION

In summary, we found that the presence of Cu2+ accelerated the oxidation process of BP. The enhancement was attributed to the fact that the presence of Cu2+ promoted the bonding of oxygen on the BP surface and then the desorption of phosphate molecules from the BP surface. The Cu2+ themselves undergo dynamic changes during the reaction. Our results improve the understanding of BP oxidation and provide new ideas for the application of BP in stability studies and drug nanocarrior ablation studies.

MATERIALS AND METHODS

Materials

BP crystals were acquired from XFNANO Materials Tech Co., Ltd. in Nanjing, China, and subsequently transferred into a brown bottle within an argon-filled glove box. Additional chemicals were procured from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China) or Sigma-Aldrich (St. Louis, MI, USA) through commercial channels. All reagents used in the experiment were of analytical grade.

Preparation of few-layer BP

BP crystals weighing 30 mg were pulverized and dispersed in 100 mL of deoxygenated ultra-pure water. The solution was subjected to sonication using a pin sonicator for 20 h at 90 W. Subsequently, the brown suspension was centrifuged at 3000 r/min for 10 min to eliminate bulk BP, and the resulting supernatant was retained for subsequent analysis.

Characterization of BP

The morphology and size of BP were analyzed using TEM (FEI Tecnai F20, USA) with a molybdenum network as the substrate and AFM (Bruker USA) with a mica sheet as the substrate. The hydrodynamic size distribution of BP was determined using a Zetasizer (Nano ZS, Britain). The Raman spectra were acquired using a Raman spectrometer (LabRam HR Evolution) with 532 nm laser excitation.

Assessment of oxidation of BP at different conditions

The experiments were conducted in 8 mL centrifuge-tube batch reactors that were vibrated on a rotary shaker operating at 100 r/min. A 3-mL reaction solution was prepared in ultrapure water containing a BP suspension with an absorbance of 0.5, and 20 μmol/L of metal ions, including Mn2+, Mg2+, Ca2+, Zn2+, Co2+, Na2+, Fe3+, and Cu2+. Subsequently, metal ions were introduced into each reactor to commence the reaction. Controls were established by utilizing a reactor that was identical but lacked metal ions. The solution was sampled at specified time intervals (0, 2, 4, 8, 12, and 24 h) and promptly analyzed using the UV-vis absorption spectrometer (UV-5000) for measurement. The suspension underwent sonication prior to UV-vis measurements in order to minimize the impact of flake-restacking during the measurement.

Experiments were carried out using an identical reactor device and procedure as previously outlined to examine the influence of temperature and pH on the oxidation of BP facilitated by metal ions. The temperature gradient was established at 4, 25, 40, and 60°C. Buffer solutions with pH values of 3, 5, 7, 9, and 11 were employed to investigate the impact of pH on the BP-Cu system, replacing the initial water. Following the experiment, the pH of the solution was re-measured.

Characterization of BP during oxidation

Raman spectroscopy was employed to analyze the freshly prepared BP following a 2-h reaction with Cu2+. The X-ray photoelectron spectroscopy (XPS) spectrum was obtained using an X-ray photoelectron spectroscopy instrument from Thermo Fischer, USA. The BP suspension was deposited onto the filter paper of a vacuum suction filtration system and subsequently stored in a glove box prior to XPS characterization, with varying reaction times. During the XPS test, the sweep parameter was set to 10 with a step of 0.1. The TEM (FEI Tecnai F20, USA) was employed to examine the morphology of BP in a Cu2+ solution at 0 and 2 h. Additionally, EDS-mapping analysis was conducted to differentiate the chemical element content on the surface of BP during the reaction. The oxidation behavior of BP under the influence of Cu2+ was characterized using in situ AFM (Cyper ES, Asylum Research) with the BL-AC40TS probe model (Olympus). The probes underwent calibration for elastic modulus in air and sensitivity in the liquid environment prior to characterization. Subsequently, the BP was deposited onto the surface of the freshly peeled mica sheet. Following the absorption of BP, the mica sheet’s surface was rinsed with ultrapure water, and subsequently, 100 μL of water was added to establish a liquid environment. The light tapping technique was employed to scan the surface of BP in order to identify an appropriate sample for use as a control. A 1-mL syringe was attached to the submerged perfusion holder, and the water on BP was substituted with a Cu2+ solution. The procedure was conducted thrice using a liquid injection volume of 100 μL. BP was monitored for a duration of 1 h following readjustment of the laser.

Characterization of the oxidation products of BP

The experiments were conducted in 8 mL centrifuge-tube batch reactors that were vibrated on a rotary shaker operating at 100 r/min. A 3-mL reaction solution was prepared in ultrapure water containing a BP suspension with an absorbance of 0.5 and 20 mmol Cu2+. At specified time points (0, 2, 4, 8, 12, and 24 h), the solution was drawn into a 1-mL syringe and subsequently filtered through a 0.22-μm needle filter to eliminate the incompletely oxidized BP sheet. The filtrate was collected for subsequent analysis of anion form and content using ion chromatography (ICS-5000, Thermo, USA). The experiments utilized a 30 mmol/L KOH solution as the eluent. The control group was established without Cu2+ in the BP solution. In order to ensure that the oxidation products were within the detectable range, the oxidation time of BP was extended due to the slow oxidation rate of the system. Consequently, the sampling intervals for BP oxidation in the absence of Cu2+ were established at 0, 3, 6, and 9 days.

Computational methods

The DFT calculations were conducted using the Vienna Ab initio Simulation Package (VASP) [32,33]. The optB88-vdW functional [34] was utilized to incorporate the van der Waals forces. The formation energy of H3POx can be determined through calculation as described in reference [16].

The chemical equation can be represented as follows:

BP + a OH + b H + c O = BP-H 3 PO x   x = 2 , 3 , 4 a = 2 ,   b = 1 ,   c = 0 ,  and  x = 2 ; a = 3 ,   b = 0 ,   c = 0 ,  and  x = 3 ; a = 3 ,   b = 0 ,   c = 1 ,  and  x = 2.

The climbing image nudged elastic band (CI-NEB) method was employed to determine the activation barrier for desorption from the BP and Cu-doped BP substrate [35]. Five images were included between the initial and final state in order to investigate the transition state. The structure was optimized iteratively until the magnitude of the force acting on each atom was reduced to less than 0.05 eV/Å. The two-dimensional Brillouin zone was sampled using a 5 × 6 × 1 mesh, following the Monkhorst-Pack method [36]. The BP slab was simulated using a 3 × 2 supercell. In order to prevent interlayer interaction, a vacuum of more than 10 Å was introduced between the slabs.

Data analysis

Each experiment was conducted three times under each condition, and the reported values represent the means ± standard deviation of the three parallel experiments. All statistical analyses were conducted using Statistical Packages for the Social Sciences (SPSS) Version 19.03.

Data availability

The original data are available from corresponding authors upon reasonable request.

Acknowledgments

The authors are grateful to the editors and the anonymous reviewers for their insightful comments and suggestions.

Funding

This work was supported by the National Natural Science Foundation of China (22125602, U2067215, 22206087 and 22076078) and the National Key R&D Program of China (2022YFC3701402).

Author contributions

Z.Z. performed the experiments. Z.Z. and L.M. conceived the project and contributed to the design of the experiments and analysis of the data. S.Y. and W.L. performed the DFT calculations. All the authors discussed the results and commented on the manuscript.

Conflict of interest

The authors declare no conflict of interest.

Supplementary information

Supplementary file provided by the authors. Access here

The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.

References

  • Zheng F, Chen Z, Li J, et al. A highly sensitive crispr-empowered surface plasmon resonance sensor for diagnosis of inherited diseases with femtomolar-level real-time quantification. Adv Sci 2022; 9: e2105231. [Article] [Google Scholar]
  • Chen Z, Wu C, Yuan Y, et al. CRISPR-Cas13a-powered electrochemical biosensor for the detection of the L452R mutation in clinical samples of SARS-CoV-2 variants. J Nanobiotechnol 2023; 21: 141. [Article] [Google Scholar]
  • Chen Z, Li J, Li T, et al. A CRISPR/Cas12a-empowered surface plasmon resonance platform for rapid and specific diagnosis of the Omicron variant of SARS-CoV-2. Natl Sci Rev 2022; 9: nwac104. [Article] [Google Scholar]
  • Qu G, Xia T, Zhou W, et al. Property-activity relationship of black phosphorus at the nano-bio interface: From molecules to organisms. Chem Rev 2020; 120: 2288-2346. [Article] [Google Scholar]
  • Tao W, Zhu X, Yu X, et al. Black phosphorus nanosheets as a robust delivery platform for cancer theranostics. Adv Mater 2017; 29: 1603276. [Article] [NASA ADS] [CrossRef] [Google Scholar]
  • Yang B, Yin J, Chen Y, et al. 2D-black-phosphorus-reinforced 3D-printed scaffolds: A stepwise countermeasure for osteosarcoma. Adv Mater 2018; 30: 1705611. [Article] [NASA ADS] [CrossRef] [Google Scholar]
  • Shao J, Xie H, Huang H, et al. Biodegradable black phosphorus-based nanospheres for in vivo photothermal cancer therapy. Nat Commun 2016; 7: 12967. [Article] [Google Scholar]
  • Wild S, Fickert M, Mitrovic A, et al. Lattice opening upon bulk reductive covalent functionalization of black phosphorus. Angew Chem Int Ed 2019; 58: 5763-5768. [Article] [CrossRef] [PubMed] [Google Scholar]
  • van Druenen M. Degradation of black phosphorus and strategies to enhance its ambient lifetime. Adv Mater Inter 2020; 7: 2001102. [Article] [CrossRef] [Google Scholar]
  • Peng L, Abbasi N, Xiao Y, et al. Black phosphorus: Degradation mechanism, passivation method, and application for in situ tissue regeneration. Adv Mater Inter 2020; 7: 2001538. [Article] [CrossRef] [Google Scholar]
  • Niu X, Li Y, Zhang Y, et al. Photo-oxidative degradation and protection mechanism of black phosphorus: Insights from ultrafast dynamics. J Phys Chem Lett 2018; 9: 5034-5039. [Article] [Google Scholar]
  • Zhou Q, Chen Q, Tong Y, et al. Light-induced ambient degradation of few-layer black phosphorus: mechanism and protection. Angew Chem Int Ed 2016; 55: 11437-11441. [Article] [CrossRef] [PubMed] [Google Scholar]
  • Zhang S, Zhang X, Lei L, et al. Ph-dependent degradation of layered black phosphorus: Essential role of hydroxide ions. Angew Chem Int Ed 2019; 58: 467-471. [Article] [CrossRef] [PubMed] [Google Scholar]
  • Plutnar J, Sofer Z, Pumera M. Products of degradation of black phosphorus in protic solvents. ACS Nano 2018; 12: 8390-8396. [Article] [CrossRef] [PubMed] [Google Scholar]
  • Wang Y, Yang B, Wan B, et al. Degradation of black phosphorus: A real-time 31P NMR study. 2D Mater 2016; 3: 035025. [Article] [CrossRef] [Google Scholar]
  • Zhang T, Wan Y, Xie H, et al. Degradation chemistry and stabilization of exfoliated few-layer black phosphorus in water. J Am Chem Soc 2018; 140: 7561-7567. [Article] [Google Scholar]
  • Long J, Yao Z, Zhang W, et al. Regulation of osteoimmune microenvironment and osteogenesis by 3D-printed PLAG/black phosphorus scaffolds for bone regeneration. Adv Sci 2023; 10: 2302539. [Article] [Google Scholar]
  • Xu Y, Mo J, Wei W, et al. Oxidized black phosphorus nanosheets as an inorganic antiresorptive agent. CCS Chem 2021; 3: 1105-1115. [Article] [Google Scholar]
  • Li Y, Fang Q, Sheng JYH, et al. Cancer cell-specific autophagy activation using phosphorus-based nanoplatform as anabolism activator. ACS Mater Lett 2023; 5: 2028-2038. [Article] [CrossRef] [Google Scholar]
  • Zoroddu MA, Aaseth J, Crisponi G, et al. The essential metals for humans: A brief overview. J Inorg Biochem 2019; 195: 120-129. [Article] [Google Scholar]
  • Chen W, Ouyang J, Yi X, et al. Black phosphorus nanosheets as a neuroprotective nanomedicine for neurodegenerative disorder therapy. Adv Mater 2018; 30: 1703458. [Article] [NASA ADS] [CrossRef] [Google Scholar]
  • Guo Z, Chen S, Wang Z, et al. Metal-ion-modified black phosphorus with enhanced stability and transistor performance. Adv Mater 2017; 29: 1703811. [Article] [NASA ADS] [CrossRef] [Google Scholar]
  • Shao X, Ding Z, Zhou W, et al. Intrinsic bioactivity of black phosphorus nanomaterials on mitotic centrosome destabilization through suppression of PLK1 kinase. Nat Nanotechnol 2021; 16: 1150-1160. [Article] [Google Scholar]
  • Ahmed T, Balendhran S, Karim MN, et al. Degradation of black phosphorus is contingent on UV-blue light exposure. npj 2D Mater Appl 2017; 1: 18. [Article] [Google Scholar]
  • Favron A, Gaufrès E, Fossard F, et al. Photooxidation and quantum confinement effects in exfoliated black phosphorus. Nat Mater 2015; 14: 826-832. [Article] [Google Scholar]
  • Khatami SH, Vakili O, Movahedpour A, et al. Laccase: Various types and applications. Biotech App Biochem 2022; 69: 2658-2672. [Article] [CrossRef] [PubMed] [Google Scholar]
  • Mo J, Xie Q, Wei W, et al. Revealing the immune perturbation of black phosphorus nanomaterials to macrophages by understanding the protein corona. Nat Commun 2018; 9: 2480. [Article] [Google Scholar]
  • Alsaffar F, Alodan S, Alrasheed A, et al. Raman sensitive degradation and etching dynamics of exfoliated black phosphorus. Sci Rep 2017; 7: 44540. [Article] [Google Scholar]
  • Wu S, He F, Xie G, et al. Black phosphorus: Degradation favors lubrication. Nano Lett 2018; 18: 5618-5627. [Article] [Google Scholar]
  • van Druenen M, Davitt F, Collins T, et al. Evaluating the surface chemistry of black phosphorus during ambient degradation. Langmuir 2019; 35: 2172-2178. [Article] [Google Scholar]
  • Wang H, Yang X, Shao W, et al. Ultrathin black phosphorus nanosheets for efficient singlet oxygen generation. J Am Chem Soc 2015; 137: 11376-11382. [Article] [Google Scholar]
  • Kresse G, Furthmüller J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput Mater Sci 1996; 6: 15-50. [Article] [Google Scholar]
  • Kresse G, Furthmüller J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys Rev B 1996; 54: 11169-11186. [Article] [Google Scholar]
  • Klimeš J, Bowler DR, Michaelides A. Chemical accuracy for the van der Waals density functional. J Phys-Condens Matter 2010; 22: 022201. [Article] [Google Scholar]
  • Henkelman G, Uberuaga BP, Jónsson H. A climbing image nudged elastic band method for finding saddle points and minimum energy paths. J Chem Phys 2000; 113: 9901-9904. [Article] [Google Scholar]
  • Monkhorst HJ, Pack JD. Special points for Brillouin-zone integrations. Phys Rev B 1976; 13: 5188-5192. [Article] [Google Scholar]

All Figures

thumbnail Figure 1

Characterization of the prepared BP. (a) TEM image of few-layered BP. (b) HRTEM image of BP. The inset image showed the corresponding SAED pattern. (c) Raman spectrum of BP. (d) AFM image of BP. (e) The height profiles of BP along the white lines in (c). (f) Histogram of BP size distribution. The histograms were developed by counting 200 sheets for each sample, with Gaussian fit curves shown in each histogram.

In the text
thumbnail Figure 2

(a) Oxidation of BP over time with different kinds of metal ions. (b) Oxidation rates of BP at different Cu2+ concentrations. (c) Pseudo-first-order rate plots for oxidation of BP. (d) Relationship between pseudo-first-order rate constants and Cu2+ concentration. (b–d) Experimental conditions were as follows: the absorbance of BP was 0.5, [Cu2+] = 1–20 μmol/L, pH = 7.0, 25°C. Error bars represent standard deviations (n = 3).

In the text
thumbnail Figure 3

Characterization of BP during the reaction. (a) Raman spectra of BP in 20 μmol/L Cu2+ solution at 0 and 2 h. (b) XPS spectra of BP exposed to Cu2+. The morphology of the BP sheet at 0 h (c) and 2 h (d) after reaction with Cu2+. The white tip indicates the complete edge of the BP sheet. The yellow tip indicates the rounded edge after partial oxidation, and the red circle indicates the black spots loaded on the surface of BP. (e) In situ AFM images acquired with Cu2+ at different times, showing the morphology evolution of a BP sheet. (f) Height profiles of the BP nanoflake acquired along the dashed lines in panel (e).

In the text
thumbnail Figure 4

Relative concentrations of PO43−, PO33− and PO23− compared to the values at the initial state measured by IC in the absence of Cu2+ (a) and in the presence of Cu2+ (c). Mole fractions of PO43−, PO33−, and PO23− were measured at different storage times in the absence of Cu2+ (b) and in the presence of Cu2+ (d).

In the text
thumbnail Figure 5

The mechanism of rapid oxidation of BP in the presence of Cu2+.

In the text
thumbnail Figure 6

(a) Bind capacity of BP nanosheets to different metal ions. (b) Adsorption kinetics curve of BP on the Cu2+. (c) XPS spectra of BP nanosheets before and after Cu adsorption for 1 h. (d) Schematic diagram of oxygen molecule adsorption on the surface of BP before and after Cu adsorption.

In the text
thumbnail Figure 7

(a) Structure of the formed H3POx and the corresponding formation energies for pristine BP. (b) Structure of the formed H3POx and the corresponding formation energies for Cu@BP. (c) Desorption barrier of H3POx from BP calculated by CI-NEB method. (d) Desorption barrier of H3POx from Cu@BP calculated by CI-NEB method.

In the text

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