【JACS】东北大学徐大可、杨波、李祥宇|吸收率近 100%！λ-Ti₃O₅纳米颗粒打造超强光热防污新材料
文章标题：Flatband λ-Ti₃O₅ Nanoparticles Unlocking Near-Unity Solar Absorptivity for Ultrarobust Photothermal Antibiofouling
通讯作者：Xiangyu Li、Bo Yang、Dake Xu
文章概要
引言
生物污损是微生物生物膜在材料表面附着堆积引发的棘手问题，微生物代谢会直接造成材料损毁，对工业系统、海洋基础设施以及全球公共卫生都带来极大威胁。传统抗菌药剂是抑制微生物繁殖的常用手段，但长期不合理使用会诱导细菌产生抗菌耐药性，而生物膜内部的胞外聚合物会形成致密保护屏障，让膜内细菌的耐受能力比游离细菌高出上千倍，进一步加重生物污损治理难度。如今光热防污技术凭借作用精准、不催生耐药性、适用范围广等特点成为热门研究方向，各类金属、碳基、半导体光热材料陆续被研发，但现有材料大多只能响应窄波段光谱，无法充分利用自然光，同时还存在生物安全性差、长期使用易老化失稳等缺陷。钛低价氧化物拥有可调控的电子结构与光学性能，其中λ-Ti₃O₅微米粉体此前已被证实具备优秀的太阳能吸收能力，可微米形貌难以适配生物界面相关应用。再加上 Ti₃O₅拥有多种晶型，传统制备方式很难合成高纯度纳米级 λ-Ti₃O₅，高温制备过程还容易造成晶粒长大，这些问题都限制了该材料的发展，基于此，本研究围绕纳米 λ-Ti₃O₅的制备与光热防污性能展开深入探究。
Figure 1. Fabrication process and characterization of the λ-Ti3O5 NPs. (a) Schematic illustration of the preparation procedures and antibiofouling behavior of the λ-Ti3O5 NPs. (b) SEM image of the λ-Ti3O5 NPs showing the uniform nanosphere morphology. (c) TEM images of the λ-Ti3O5 NPs and corresponding EDS analysis indicating the distribution of Ti and O elements. (d, e) High-resolution TEM image and SAED pattern of the λ-Ti3O5 NPs. (f) Dynamic light scattering size distribution of the λ-Ti3O5 NPs. (g) XPS wide spectra and (h) high-resolution XPS spectra of Ti 2_p_ of the λ-Ti3O5 NPs. (i) XRD patterns of the TSO products obtained at different Ti–C atomic ratios. (j) Phase diagram of the structure of the synthesized products as a function of Ti–C atomic ratio, reduction temperature, and H2 flow rate, together with the corresponding optimized crystal structures.
主要实验及结论
研究团队搭建了溶胶 - 凝胶结合高温氢气还原的合成体系，利用超分子纳米支架的空间限域作用，突破了高纯度、形貌规整的 λ-Ti₃O₅纳米颗粒合成瓶颈。团队逐一探究 Ti-C 原子比、还原温度、氢气流量三大关键参数对产物晶相、形貌的影响，最终确定最优合成条件为 Ti-C 原子比 1:2.2、烧结温度 1200–1230 ℃、氢气流量 0.3 L・min⁻¹，最终得到平均粒径约40 nm、单分散性优异的球形 λ-Ti₃O₅纳米颗粒。借助扫描电镜、透射电镜、X 射线衍射、X 射线光电子能谱等多种表征技术对产物进行验证，结果证明所得样品为纯相 λ-Ti₃O₅，材料中 Ti³⁺与 Ti⁴⁺的比例和理论数值高度吻合，也证实这套合成方法可以精准调控钛低价氧化物的晶相与微观结构，并不是简单将传统微米材料做尺寸缩减。
Figure 2. Evaluation of photothermal effect of the λ-Ti3O5 NPs. Band structure and calculated PDOS of (a) anatase TiO2 and (b) λ-Ti3O5. (c) UV–vis–NIR spectra of λ-Ti3O5 NPs, β-Ti3O5 NPs, λ-Ti3O5 MPs, β-Ti3O5 MPs, and TiO2 over 250–2500 nm, together with the normalized spectral solar irradiance density of air mass 1.5 global (AM 1.5 G) tilt solar spectrum. (d) Temperature evolution of the λ-Ti3O5 NPs under different irradiation intensities. (e) Infrared images of the λ-Ti3O5 NPs after 0 and 300 s of irradiation under one-sun illumination. (f) Recycling-heating profiles of the λ-Ti3O5 NPs under one sun irradiation for five light-on/off cycles. (g) Photothermal stability of the λ-Ti3O5 NPs after exposure to various organic solvents.
研究结合第一性原理计算分析材料电子特性，发现 λ-Ti₃O₅内部的Ti-Ti 二聚体会在费米能级附近形成平带结构，大幅提升体系联合态密度，让材料实现全光谱近 100% 的太阳能吸收率。对比测试结果显示，和 β 相 Ti₃O₅、常规 TiO₂以及微米级 λ-Ti₃O₅相比，纳米 λ-Ti₃O₅的光捕获能力额外提升 4%，光热转换效率相比微米样品提高约8%，整体太阳能 - 热能转换效率达到 99.8%。在标准模拟太阳光照射下，该纳米材料 300 秒内就能快速升温至 75 ℃以上，光热响应十分迅速；经过多次光照循环、有机溶剂浸泡以及酸碱高盐环境处理后，材料的晶体结构和光热性能都没有明显衰减，具备极佳的循环使用能力与化学稳定性。
Figure 3. Photothermal antibacterial performance of the λ-Ti3O5 NPs. (a) Schematic diagram of the λ-Ti3O5 NPs killing planktonic bacteria via photothermal effect (created with BioGDP.com). Viable planktonic bacteria quantities of (b) S. aureus, (c) E. coli, (d) B. vietnamensis, and (e) P. aeruginosa after incubation with different concentrations of Ti3O5 powders with various crystal phases and particle sizes under dark and simulated solar irradiation conditions in enrichment media. (f) CLSM images of planktonic cells of S. aureus and E. coli after incubation with different concentrations of the λ-Ti3O5 NPs under dark and simulated solar irradiation conditions. The data are presented as mean values ± SD, n = 3, ***p < 0.001.
实验选用金黄色葡萄球菌、大肠杆菌、越南芽孢杆菌、铜绿假单胞菌等多种典型革兰氏阳性菌、革兰氏阴性菌与海洋污损细菌，全面评测材料的光热抗菌和抗生物膜效果。在避光环境中，不同浓度的 λ-Ti₃O₅纳米颗粒都不会抑制细菌正常生长，表现出良好的生物相容性；而在模拟太阳光照射后，材料展现出强大的广谱杀菌能力，即便使用低至 50 μg/mL的浓度，也能让各类细菌活菌数量下降 4 个数量级以上。针对清除难度极高的成熟生物膜，该材料同样效果突出，200 μg/mL 浓度下对两种典型细菌生物膜的清除效率超过 99.9%，连续进行 20 轮循环处理后，材料的抗菌抗污效率依旧保持在 98% 以上，能够长期反复投入使用。
Figure 4. Photothermal antibiofilm performance of the λ-Ti3O5 NPs. (a) Schematic diagram of the λ-Ti3O5 NPs destroying biofilms via photothermal effect (created with BioGDP.com). Viable biofilm sessile cell quantities of (b) S. aureus and (c) E. coli after incubation with different concentrations of Ti3O5 powders with various crystal phases and particle sizes under dark and simulated solar irradiation conditions in enrichment media. (d) CLSM images of biofilms formed by S. aureus and E. coli in the presence of different concentrations of the λ-Ti3O5 NPs under dark and simulated solar irradiation conditions. Time-dependent antibiofouling performance evaluated by the viable counts of (e) S. aureus and (f) E. coli after incubation with different concentrations of λ-Ti3O5 NPs under light treatment. The data are presented as mean values ± SD, n = 3, ***p < 0.001.
团队结合微观形貌观测、电位检测、活性氧表征以及全原子分子动力学模拟，理清了 λ-Ti₃O₅纳米颗粒三重协同的光热防污机制。中性环境下 λ-Ti₃O₅纳米颗粒表面带正电，依靠静电吸附紧密附着在带负电的细菌表面，为后续杀伤作用创造条件；光照会激发材料产生大量高毒性活性氧，直接破坏细菌 DNA 与胞内活性物质，造成氧化损伤；局部光热效应提升环境温度后，细菌细胞膜脂质的扩散系数提升 7.4 倍，细胞膜流动性显著增强且分布变得杂乱不均，膜厚度随之减小，细胞膜结构彻底失去稳定性。三重机制相互配合，全面瓦解细菌生存体系，该材料的有效使用剂量比当下主流光热防污材料低 20 倍，综合性能优势十分突出。
Figure 5. Principles underlying the synergistic antibiofouling behavior of the λ-Ti3O5 NPs. (a) Morphology of planktonic and sessile S. aureus and E. coli incubated with λ-Ti3O5 NPs at a concentration of 200 μg mL–1 under light irradiation. (b) Zeta potentials of λ-Ti3O5 NPs under different pH conditions. (c) Zeta potentials of the λ-Ti3O5 NPs, S. aureus, E. coli, B. vietnamensis, and P. aeruginosa in water. (d) CLSM images of endogenous ROS generated in S. aureus and E. coli upon treatment with λ-Ti3O5 NPs under light condition. Spatial distribution heatmaps of tracer diffusion coefficients (_D_t) of lipid headgroup atoms on the membrane surface at (e) 301.15 K and (f) 348.15 K, with the corresponding color bars shown on the right. (g) Mean square displacement (MSD) curves of all lipid headgroup atoms as a function of time at two temperatures. The fitting tracer diffusion coefficients (unit: nm2 ns–1) are indicated above the corresponding lines. (h, i) Comparison of the membrane thickness in systems undergoing ROS-induced phospholipid peroxidation at different temperatures. In the structural diagram, pink and blue spheres represent P and N atoms, respectively, while green and orange chains represent the hydrophobic tails of the upper and lower lipid layers. Water molecules are distributed on both sides of the bilayer membrane. (j) Comparison of the antibiofouling performance of λ-Ti3O5 NPs with other representative reported antibiofouling materials (Table S3).
总结及展望
本研究成功实现了高纯度纳米尺度λ-Ti₃O₅的可控制备，充分发挥 Ti-Ti 二聚体诱导的平带结构与纳米尺寸效应的协同作用，研发出一款集超高光吸收效率、优异光热转换能力、长期稳定性、广谱抗菌抗生物膜性能于一体的新型纳米材料。这项工作不仅解决了纯相纳米 λ-Ti₃O₅难以制备的长期难题，也明确了平带结构在优化光热抗菌材料性能中的关键价值。该材料凭借出众的综合表现，有望在海洋防污、工业设备防护等实际场景中落地应用，同时也为生物医药、生物催化、环境修复等多个领域，设计新一代光响应功能纳米材料提供了全新的思路与可行的构建范式。