Designing biomimetic two-dimensional channels for uranium separation from seawater

Efficient separation of uranium from seawater stands as a pivotal challenge. This study unveils an approach focusing on the ingenious design of biomimetic two-dimensional (2D) membranes tailored explicitly for this purpose. Leveraging the unique interplay of DNA strands housing U aptamers, pH-responsive i-motifs, and poly A(10) segments ingeniously embedded within graphene oxide membranes, a distinctive biomimetic 2D channel is engineered. The strategic integration of these bio-inspired elements enables dynamic adjustment of interlayer spacing, augmenting both the permeability of the membrane and the selectivity of the aptamer for uranyl ions. During the separation process, the encounter between uranyl ions and the enhanced aptamer within the interlayers initiates a crucial interaction, triggering a specific concentration polarization mechanism. This mechanism stands as the cornerstone for achieving a highly selective separation of uranyl ions from the vast and complex matrix of seawater. The membrane exhibits excellent performance in real seawater, with a rejection rate of uranyl ions of ≈100% and sustained selectivity of uranyl ions over ten cycles. Importantly, the selectivity of uranium and vanadium can reach 14.66. The significance of this research lies not only in the effective separation of uranyl ions but also in showcasing the broader applicability of 2D membrane design in chemical engineering.


Introduction
2][3] Uranium remains the predominant fuel source for most nuclear power plants. 4,5Conventionally, uranium extraction has been predominantly reliant on underground deposits. 6,7However, the limited reserves of such deposits necessitate the exploration of alternative uranium sources.Seawater presents a viable option as it contains minute concentrations of uranium (approximately 3.3 ppb). 8,9Given the vast volume of seawater, the total uranium resource potential is staggering, estimated to be approximately 4.5 billion tons, surpassing land-based proven uranium reserves by several orders of magnitude. 6Harnessing uranium resources from the ocean in an efficient manner holds substantial promise for the sustainable advancement of nuclear power.4][15][16] However, developing a highly selective and permeable membrane for uranium extraction from seawater presents a signicant challenge.
A two-dimensional (2D) lamellar membrane represents a separation membrane constructed through the sequential stacking of 2D nanosheets. 14The interlayer channels, emerging from the stacking arrangement between these nanosheets, facilitate the swi and discerning transport of small molecules. 17Consequently, the 2D lamellar membrane stands as an exemplary medium for the separation of small molecules. 13raphene oxide (GO), a prominent derivative of graphene, assumes a crucial role as a 2D constituent within these lamellar membranes. 18The GO membrane, owing to its commendable mass transfer capabilities, has garnered considerable attention from researchers in recent years and undergone comprehensive development.][21][22][23][24][25][26][27][28][29] Despite the sustained advancements in the realm of small molecule separation achieved by 2D lamellar membranes, a universally accepted theoretical framework for elucidating the separation mechanisms remains elusive. 15Predominantly, extant theories underscore the signicance of the size screening effect in facilitating the selective separation of 2D lamellar membranes. 30][33][34] Recent investigations reveal that metal ions possess the capability to permeate the interlayer space of the GO membrane, thereby exerting inuence over its interlayer spacing. 19In scenarios involving mixed ion systems, the determination of the GO membrane's interlayer spacing hinges upon the initial entry of metal ions into the interlayer space. 35However, the exible nature of materials such as GO implies that the size screening effect alone fails to comprehensively account for all observed separation phenomena.Consequently, it is imperative to posit the existence of an alternative separation mechanism beyond the connes of the size screening effect.
Aptamers, DNA or RNA fragments capable of specic molecular recognition, were initially discovered in 1994 and have since found extensive utility in trace metal ion detection. 36,37Lu et al. employed a combinatorial biology approach to successfully isolate the uranyl ion recognition aptamer (U Aptamer), notable because of its high specicity towards uranyl ions (UO 2

2+
) and its applicability in detecting minute quantities of this species. 38ecently, Wang et al. harnessed the U Aptamer in uranium extraction from seawater, yielding promising outcomes. 40][41][42] Specically, its secondary structure remains negligible under alkaline conditions, whereas it adopts a quadruplex conguration under acidic environments, with increased folding propensity correlating with heightened acidity.Moreover, DNA molecules exhibit adsorption onto GO surfaces via p-p interactions primarily involving nitrogenous bases.Notably, purine bases (such as adenine and guanine) bind more strongly than pyrimidine bases (such as cytosine and thymine), as evidenced by research ndings. 43n this study, a designed DNA chain comprising poly A (10) , i-motif, and U Aptamer was employed (Scheme 1a). 44The DNA chain was strategically inserted between the layers of GO.The poly A (10) chains demonstrated an affinity to the GO surface through p-p interactions.The inclusion of an ion-binding aptamer enhanced membrane selectivity, while the i-motif played a pivotal role in dynamically adjusting the spacing between GO layers based on the system pH, thereby regulating permeability (Scheme 1b).Following the introduction of the DNA construct, a notable inhibition in the transmembrane transport of UO 2 2+ was observed.Intriguingly, the transmembrane transport of VO 2+ remained unaffected.Under optimal conditions, the U/V separation factor (SF) reached a noteworthy value of 14.66.A novel separation mechanism is proposed to elucidate this distinctive phenomenon, providing valuable insights into the separation mechanisms governing 2D lamellar membranes.The outcomes of this research not only bear signicance for the tailoring of 2D lamellar membranes but also extend their impact to the broader realm of advancing separation technologies within the chemical eld.

Results and discussion
Interaction and stability between GO and DNA GO was synthesized using a modied Hummers' method.The DNA chains used in the experiment were purchased directly from Suzhou Biosyntech Co., Ltd the separation strategy employed.Subsequently, GO-DNA membranes were prepared through the negative pressure suction ltration method.DNA becomes adsorbed onto the GO surface via p-p stacking interactions between DNA bases and GO, as illustrated in Fig. 1a.6][47] The absence of UV absorption at a wavelength of 260 nm in the ltrate during membrane preparation (ESI, † Fig. S3) indicates the complete immobilization of all DNA strands within the membrane.The morphology of DNA molecules at different pH levels (pH = 2, 4, 6, and 8) was characterized using atomic force microscopy (AFM).At pH = 2, the phosphodiester bond of the DNA molecule undergoes hydrolysis, resulting in shorter fragments and an irregular AFM image (Fig. 1b).Mass spectrometry results conrm the hydrolysis of DNA molecules (ESI † Fig. S4).Chainlike DNA molecules are observable at other pH values (pH = 4, 6, and 8).Furthermore, a mixture of GO and DNA was analyzed using AFM and transmission electron microscopy (TEM).AFM images reveal a similar phenomenon to DNA on the GO surface (Fig. 1c).Chain-like structures were observed on the GO surface at mild pH (pH = 4, 6, and 8), while irregularities were observed at pH = 2. AFM images also conrm the distribution of DNA molecules between the two layers of GO, signifying the successful insertion of DNA molecules between the GO layers.TEM images further support this observation (Fig. 1d).To eliminate the interference caused by GO folds, TEM images of GO were employed for comparative analysis (ESI, † Fig. S5).Notably, GO folds exhibit broader and longer features, coupled with a comparatively lower density of surface wrinkles at equivalent magnications compared to the blend.This validation substantiates the identity of the numerous chain structures observed in the TEM images of GO and DNA mixtures as unequivocally DNA molecules.It is noteworthy that the distribution of DNA on the GO surface is evident in both AFM and TEM images, irrespective of whether it is an intact DNA molecule or a hydrolyzed fragment.This underscores the effectiveness of the p-p interaction between GO and DNA in anchoring DNA molecules to the surface of the GO nanosheets.Moreover, the successful insertion of DNA molecules between the GO layers post-membrane preparation is highlighted.At the same time, this observation shows that the GO-DNA membrane cannot be applied to strongly acidic systems.However, the pH value of seawater is usually in the range of 7 to 8, and the GO-DNA membrane is stable under this condition.Therefore, it is feasible to apply the GO-DNA membrane to uranium extraction from seawater.
To assess the stability of the GO-DNA complex, the GO-DNA membrane was immersed in aqueous solutions with varying pH values (pH = 2, 4, 6, and 8) for different durations.The resulting solutions were subjected to analysis using UV spectroscopy and gel electrophoresis.Remarkably, no DNA bands were observed even aer 7 days of immersion (ESI, † Fig. S6), and there was no discernible UV absorption at 260 nm (ESI, † Fig. S7).This observation underscores the efficacy of the p-p interaction between DNA bases and GO in securely anchoring DNA molecules between the GO layers.Importantly, this stability persists even when the DNA molecules undergo hydrolysis, preventing their leaching from the GO layers.

Regulation of GO layer spacing and transmittance by DNA
GO and GO-DNA membranes were immersed in solutions with different pH values (pH = 2, 4, 6, and 8) for 12 hours, dried and then analyzed using X-ray diffraction (XRD, Fig. 2a).Upon the incorporation of DNA, the (001) peak (∼12°) of GO shied to a lower degree, indicating an increase in the interlayer spacing of the GO membrane.The extent of the le shi of the (001) peak varied with pH.In comparison with the GO membrane, the 2q degree of the GO-DNA membrane shied le by 1°, 1.45°, 1.1°, and 0.38°at pH = 2, 4, 6, and 8, respectively (ESI, † Fig. S8).This pH-dependent change in interlayer spacing is attributed to the inuence of the pH-dependent i-motif structure.Under alkaline conditions, where the i-motif secondary structure is negligible, the expansion of the interlayer spacing is primarily attributed to the size of the DNA molecule itself.Conversely, under acidic conditions, the formation of an i-motif tetrad structure results in a signicant increase in the interlayer spacing of GO (Fig. 2c).And as the pH decreases, this folding process intensies, leading to slight differences in the interlayer spacing of GO-DNA membranes under acidic conditions.At pH = 2, DNA molecules undergo hydrolysis, and mass spectrometry data directly verify the hydrolysis of DNA molecules (ESI, † Fig. S4).Immersion experiments conrm that hydrolyzed fragments persist within the interlayer space (ESI, † Fig. S6 and S7).The widening of the interlayer spacing of GO is a result of the accumulation of these fragments post-hydrolysis, a process dictated by the inherent properties of the DNA molecule itself.
Changes in the interlayer spacing of the GO membrane directly affect its ionic transmittance.Typical monovalent ions (Na + and K + ) and divalent ions (Ca 2+ and Mg 2+ ) were used to evaluate the ionic transmittance of the GO-DNA membrane in a custom-made permeable membrane separation device (ESI, † Fig. S1a).The ionic transmittance data for the GO membrane and GO-DNA membrane under varying pH conditions are presented in ESI † Fig. S9.The growth rate of ionic transmittance was calculated to evaluate the change in ionic transmittance aer the introduction of DNA molecules (Fig. 2d).Specically, at pH = 2, the ionic transmittance of Na + increased by 19.26%, 33.78%, 19.87%, and 5.32% respectively at pH = 2, 4, 6, and 8. Similarly, the ionic transmittance of K + showed increases of 10.15%, 15.76%, 11.49%, and 3.35% at the same pH values.The ionic transmittance trends for Ca 2+ and Mg 2+ exhibited similar patterns.The inuence of pH on the interlayer spacing was highly consistent with its impact on ionic transmittance.These results suggest that DNA molecules can dynamically adjust the interlayer spacing of the GO membrane in response to the system's pH, thereby modulating its ionic transmittance.
The GO-DNA membranes were subjected to characterization under different pH values (pH = 2, 4, 6, 8) using scanning electron microscopy (SEM).The cross-section of the GO-DNA membrane reveals a distinctive "book-like" layered structure (Fig. 2b), consistent with the typical structure of GO membranes.Raman spectroscopy was employed to investigate defects in GO membranes both before and aer DNA incorporation and before and aer separation (ESI, † Fig. S10).No signicant alterations in GO defects were observed under these conditions.Fourier transform infrared spectroscopy (FT-IR, ESI, † Fig. S11) was utilized to analyze the chemical composition of both GO and GO-DNA membranes.Compared with the GO membrane, the peaks at 1240 cm −1 and 1070 cm −1 of the GO-DNA membrane are signicantly enhanced, which are attributed to P]O and P-O in the DNA molecules respectively, proving the successful introduction of DNA.

Separation performance of the GO-DNA membrane
To assess the selectivity of the GO-DNA membrane, its performance in separating uranium was examined in spiked simulated seawater.For convenience, the concentrations of Cu 2+ , Ni 2+ , Zn 2+ , and UO 2 2+ were increased by a thousand-fold (the concentrations of all ions are given in ESI † Table S1).The impact of pH on the separation efficiency of the GO-DNA membrane was investigated at pH values of 4, 6, and 8. Ionic transmittance aer a 12-hour separation experiment is presented in Fig. 3a-c.Remarkably, GO-DNA demonstrates exceptional rejection of UO 2 2+ at all tested pH levels.This underscores the outstanding separation performance of GO-DNA membranes under pH conditions conducive to the stability of DNA molecules.In certain instances, an observation of higher transmittance for divalent ions compared to monovalent ions has been documented.This occurrence can be ascribed to the disparate initial concentrations of metal ions.Specically, in spiked simulated seawater, the concentration of monovalent ions greatly surpasses that of divalent ions.While the percentage transmission of monovalent ions may seem comparatively lower than that of divalent ions, their absolute transmission capacity is substantially greater.The inuence of the added amount of DNA on the GO-DNA separation effect was further probed.The separation performance of GO-DNA membranes with different amounts of DNA added was tested in spiked simulated seawater (labeled GO-DNA-x, where x represents the amount of DNA added to the separation membrane in nmol).Ionic transmittance aer the 12-hour separation experiment is depicted in Fig. S12a, †  concentration in spiked seawater.Its separation performance was evaluated using various spiked concentrations of uranyl ions (33 ppm, 3.3 ppm, and 330 ppb, respectively).The concentrations of the remaining ions were the same as those of the spiked simulated seawater, as shown in ESI † Table S1.Ionic transmittance aer a 12-hour separation experiment is illustrated in Fig. S12b, † and the SF is shown in Fig. 3e.The transmittance of UO 2 2+ decreases as its concentration decreases, while the transmittance of other ions remains relatively stable.This signies that GO-DNA maintains excellent separation ability even at lower UO 2 2+ concentrations, indicating promising prospects for seawater applications.
Cycling stability, a crucial parameter for industrial membrane applications, was evaluated in spiked real seawater without membrane regeneration.The concentrations of all ions were the same as those of spiked simulated seawater, as shown in ESI † Table S1.Even aer undergoing ten cycles, the transmittance of all ions exhibited uctuations within a specic range, with the rate of change in ionic transmittance remaining between −40% and 40% (ESI, † Fig. S13a and b).Additionally, in the cycling stability experiment, the rejection rate of UO 2 2+ by the GO-DNA membrane remained consistent, while the SF between UO 2 2+ and coexisting ions uctuated within an established range (Fig. 3f).The concentration of UO 2 2+ in the source solution was tested to explore the UO 2 2+ capturing ability of the GO-DNA membrane (ESI, † Fig. S13c).Aer ten cycles, the UO 2 2+ concentration showed only a weak decrease.Considering that a small amount of UO 2

2+
was detected in the driving solution (ESI, † Fig. S13a), the GO-DNA membrane captures only trace amounts of UO 2

2+
. The GO-DNA membrane mainly blocks the transmembrane transport of UO 2

2+
, thereby achieving the separation of UO 2

2+
. These ndings demonstrate the excellent cycling stability of the GO-DNA membrane, highlighting its potential for practical industrial applications.At the same time, the excellent stability of the GO-DNA membrane provides additional evidence that the DNA sequence is stable during the separation process.
Pressure ltration experiments were conducted to comprehensively assess the efficacy of the GO-DNA membrane.Initially, the water permeability of the GO-DNA membrane was examined under varying concentrations of DNA.The ndings demonstrated a positive correlation between the amount of DNA incorporated and the water permeability of the GO-DNA membrane, as illustrated in Fig. S14 of the ESI.† Subsequently, the ion separation capability of the GO-DNA membrane was evaluated using spiked real seawater.The concentrations of all ions were the same as those of spiked simulated seawater, as shown in ESI † Table S1.Fig. 3g presents the ion rejection rates, while Fig. 3h illustrates the SF for coexisting ions, specically focusing on UO 2

2+
. The outcomes revealed the outstanding uranyl ion rejection capability of the GO-DNA membrane along with its notably low rejection of coexisting ions.These results underscore the superior separation performance of the GO-DNA membrane in pressure ltration experiments.
Anti-biofouling activity plays a pivotal role in the practical utilization of GO-DNA membranes.The antibacterial efficacy of the GO-DNA membrane was evaluated as per the methodologies outlined in ESI 1.12.† Both the GO membrane and the GO-DNA membrane exhibited remarkable antibacterial properties, demonstrating an antibacterial rate exceeding 98% (Fig. 4g and ESI † Table S2).This underscores the outstanding anti-biofouling performance of the GO-DNA membrane, primarily attributed to the presence of GO, 62 with the incorporation of DNA not altering this characteristic.These ndings underscore the vast potential applications of the GO-DNA membrane.The uranium-tovanadium (U/V) separation capability stands as a crucial metric for assessing the effectiveness of membranes in uranium extraction from seawater.9][50][51][52][53][54][55][56][57][58][59][60][61] The comparative analysis reveals that the GO-DNA membrane exhibits outstanding U/V separation ability, underscoring its potential as an efficient separation membrane for uranium extraction from seawater.

Separation mechanism
The GO-DNA membrane underwent rigorous scrutiny via X-ray photoelectron spectroscopy (XPS) both pre-and post-separation experimentation.Relative to the unmodied GO membrane, discernible features emerged in the XPS spectrum of the separated GO-DNA membrane at 390.00 eV and 379.00 eV, corresponding to U 4f 5/2 and U 4f 7/2 , respectively (Fig. 4a and e).Notably, the presence of uranium in the separated GO-DNA membrane was conrmed by energy-dispersive X-ray spectroscopy (EDS) mapping (Fig. 4i).This evidentiary manifestation unequivocally affirms the selective entrapment of UO 2 2+ within the interlayer interstice.High-resolution XPS analysis of the oxygen fraction before and aer separation revealed a discernible peak at 529.65 eV in the GO-DNA membrane aer separation, which was attributed to the axial oxygen of UO 2 2+ (Fig. 4b-d, f-h).In addition, in the GO-DNA membrane, the peak corresponding to the carbonyl oxygen shied from 530.00 eV to 530.40 eV, a phenomenon not observed in the GO membrane.Further examination of the high-resolution XPS spectrum of uranium in the GO-DNA membrane aer separation revealed three distinct peaks at 389.96 eV, 381.45 eV, and 379.10 eV (ESI, † Fig. S18).Importantly, these uranium peaks were absent in the GO-DNA membrane before separation.Subsequent to separation from the GO membrane, similar peaks at 389.96 eV and 379.10 eV were detectable, albeit with signicantly reduced intensity, possibly due to residual UO 2 2+ .Meanwhile, high-resolution XPS analysis of other elemental components demonstrated minimal transformation before and aer separation (ESI, † Fig. S15-S17).These ndings collectively suggest that the U Aptamer binds to UO 2 2+ through oxygen coordination, consistent with existing literature reports.The separation mechanism of the GO-DNA membrane is obviously different from the traditional size screening effect.A novel separation mechanism is proposed that emphasizes the role of selective concentration polarization induced within 2D lamellar membranes.Conventionally, the prevailing permeation theories treat the permeate uid (S 1 ) and driving uid (S 2 ) as discrete systems, with ion transport being contingent upon concentration gradients between them.However, the interlayer conguration of 2D lamellar membranes, characterized by an "S" shaped channel, necessitates a reevaluation of this conventional framework.In order to more precisely elucidate the intrinsic mass transfer process of 2D lamellar membranes, a completely new separation mechanism was proposed.It posits the twodimensional separation membrane (S M ) as an autonomous entity, beyond the conventional dichotomy of S 1 and S 2 .The ion transport trajectory in the interlayer space assumes an "S" shape, wherein ions temporarily reside within the 2D lamellar membrane.The delineation of ion transport across 2D lamellar membranes is thus articulated through two discernible stages (Fig. 4j).The rst phase involves ion diffusion from the S 1 system into the S M system, driven by concentration gradients.Given that the concentration in the S 1 system (C 1 ) surpasses that in the S M system (C M ), ions traverse from the former to the latter.Subsequently, as ions populate the S M system, a situation arises where C M exceeds the concentration in the S 2 system (C 2 ).This initiates the second stage, wherein ions diffuse from the S M system to the S 2 system.Collectively, these stages comprise the ion transit process across the 2D lamellar membrane.This conceptualization is further nuanced in the case of target ions, typied by active sites embedded in the interlayer space.For target ions, active sites induce a nuanced scenario.In the rst stage, target ions diffuse from the S 1 system into the S M system due to concentration gradients.Upon entry into the S M system, active sites recognize and immobilize the ions within the interlayer space.Despite a persisting concentration difference between the S M system and the S 2 system ðC 0 M .C 0 2 Þ, the immobilizing effect of active sites precludes the diffusion of target ions into the S 2 system.As target ions continue inltrating the S M system, C 0 M approaches C 0 1 , culminating in a scenario where the concentration difference dissipates, halting the transmembrane ion transport.In this study, UO 2 2+ initially permeated the S M system from the S 1 system.Subsequently, the addition of the 39E aptamer facilitated the selective recognition and binding of UO 2 2+ , thereby immobilizing UO 2 2+ within the S M system and preventing its translocation to the S 2 system.Equilibrium was achieved when the concentration of UO 2 2+ in the S M system equaled that in the S 1 system, halting further diffusion from the S 1 system to the S M system.The transmembrane transport of UO 2 2+ was effectively impeded by this mechanism.Notably, the diffusion of coexisting metal ions remained unhindered, facilitating their separation from UO 2 2+ .This selective binding action of the 39E aptamer resulted in the entrapment of a portion of UO 2 2+ in the S M system, as evidenced by the presence of uranium in the XPS spectrum of the GO-DNA membrane.Conversely, no coexisting ions were detected in the XPS spectrum, corroborating our hypothesis.Specically, coexisting ions will quickly diffuse into the S 2 system aer entering the S M system, resulting in only very few coexisting ions existing in the GO interlayer space (S M system).Their concentration remained below the detectable range of XPS analysis.

Conclusions
In summary, the integration of DNA chains, including poly A (10) , U Aptamer, and pH-responsive i-motif, into GO layers resulted in sophisticated DNA-intercalated GO membranes.Poly A (10)  facilitated p-p interactions, binding DNA to GO, while the pHresponsive i-motif dynamically adjusted interlayer spacing.Simultaneously, the U Aptamer enhanced GO membranes' efficacy in obstructing UO 2 2+ transport, boosting separation efficiency.A novel 2D lamellar membrane permeability separation mechanism was proposed, redening the 2D lamellar membranes as an independent system.This conceptual framework offers insights into enhanced separation effects, opening avenues for tailored 2D lamellar membranes.These modications advance the understanding of 2D lamellar membrane mechanisms, paving the way for custom separation technologies.Improved separation efficiency and the proposed model highlight the potential of GO membranes for diverse applications.Future research can focus on optimizing fabrication processes, scalability, and exploring the broader applicability of this innovative separation technology.
Scheme 1 Schematic illustration of a 2D membrane with ion recognition channels.(a) Schematic representation of DNA fragments composed of poly A (10) , U Aptamer and i-motif fragments.(b) Construction strategy of the 2D separation membrane.

Fig. 1
Fig. 1 Interaction between GO and DNA.(a) Schematic diagram of p-p stacking between DNA bases and GO.(b) AFM images of DNA at pH = 2, 4, 6 and 8.The white particles in the image are crystals of the buffer solution used to adjust the pH.AFM image (c) and TEM image (d) of the mixture of GO and DNA at pH = 2, 4, 6 and 8.

Fig. 2
Fig. 2 GO-DNA membrane interlayer spacing and pH dependence of ionic transmittance.(a) XRD characterization results of GO-DNA membranes at pH = 2, 4, 6 and 8. (b) SEM images of GO-DNA membrane sections at pH = 2, 4, 6 and 8. (c) Structure-activity relationship between the pH dependence of the i-motif structure and the interlayer space of GO-DNA membranes.(d) The percentage growth rate of the ionic transmittance of the GO-DNA membrane compared with the GO membrane at pH = 2, 4, 6 and 8.

Fig. 3
Fig. 3 Separation performance test of the GO-DNA membrane.Transmittance of the GO membrane and GO-DNA membrane in spiked simulated seawater at pH = 4 (a), pH = 6 (b) and pH = 8 (c).Separation factors after 12 hours of separation experiment of the GO-DNA membrane with different amounts of DNA added (d) and different uranium spiked concentrations (e).(f) The separation factor of the GO-DNA membrane that was recycled ten times in spiked real seawater without any treatment.(g) Ion rejection rate and (h) separation factor of the GO-DNA membrane in pressure filtration experiments at a pressure of 0.08 Mpa.(i) Antibacterial ability of the GO membrane and GO-NDA membrane.(j) Comparison of uranium and vanadium separation performance. 4,7,48-61

Fig. 4
Fig. 4 Separation mechanism.XPS analysis results of the GO membrane, GO-DNA-10 membrane and GO-DNA-20 membrane before and after the separation experiment (a) and (e) the zoomed-in results of the red box part in (a).High-resolution XPS analysis results of oxygen element in GO membranes ((b) before separation and (f) after separation), GO-DNA-10 membranes ((c) before separation and (g) after separation) and GO-DNA-20 membranes ((d) before separation and (h) after separation).(i) EDS mapping of the GO-DNA membrane after the separation.(j) Schematic diagram of ion transport across a two-dimensional membrane.
and the SF is shown in Fig.3d.As the amount of DNA added increases, the transmittance of UO 2