## 3 Results
### Monolith Stability Dependence on Ultrasonication and Drying  
Upon initial dispersion and gelation, carbon aerogels are traditionally dried by supercritical fluid drying or freeze-drying in order to remove the liquid phase without disturbing or collapsing the porous network [46; 47; 48; 49]. However, both methods are rather expensive, time-consuming, and hard to handle. With the goal of a simplified and optimized synthesis protocol, we studied the impact of ultrasonication and subsequent heat drying on the monolith' stability compared to a more traditional dispersant-aided freeze-drying approach. Hereby, we determined ultrasonic treatment prior to pressing and drying of the CNT gel as a critical factor to achieve stable and free-standing monoliths. Through the high energy impact of sonication onto the CNT suspension and the resulting shear stress, individual agglomerates can be separated, leading to a dispersion of the particles [50; 51]. Interestingly, with increasing sonication time, even swelling of the CNT network can be observed, as illustrated in Figure 4a,b. Thus, strong water uptake of the CNT network is indicated, as also discussed by [PERSON] et al. [32]. Moreover, with increasing ultrasonic impact, strong gelation of the CNT-water suspension can be triggered. After 6 min of ultrasonic treatment, the CNTs form a gel displaying no free water, as displayed in Figure 4c. However, it has to be considered that similar to harsh oxidation conditions, the high energy impact during ultrasonication can lead to scission and structural damage of the CNTs [50; 52; 53]. Thus, we additionally studied the impact of sonication-induced shear forces through TEM imaging (see Figure S3), where no significant structural effect on the CNTs could be found upon a six-minute ultrasonic treatment. Figure 4: \(Cont.\)  
Figure 3: pH-shift experiments for untreated (green) and oxidized CNT-K (blue, grey) particles at differing concentrations. The nanotubes were weighed in as dry mass. Incubation was conducted at RT for 24 h.  
In contrast to an ultrasonically steered approach, the use of dispersing agents has already established itself as a first step in the synthesis of CNT monoliths [11, 15, 16, 17]. However, utilization of dispersants introduces an additional component to the monoliths' network, further influencing its adsorptive properties, as shown by [PERSON] et al. for pristine CNTs [54]. Introducing nanotube gelation through ultrasound, the addition of surfactants disturbed the gelation process in our system (see Figure 4d). Here, the utilized dispersant SDBS strongly accumulated on the surface of the nanotubes during ultrasonication, leading to sterical separation and inhibition of gel formation (see Figure S3d) [55, 56]. Consequently, we were able to proceed with our synthesis without additional dispersing agents. Heat drying the sonicated and pressed CNT-gel, we found that the resulting monoliths remained intact with increasing sonication time even after prolonged water incubation and shaking of the sample container (see Figure 5a). For instance, upon a heat drying approach, the synthesized monoliths showed no sign of disintegration in DI-water even after 6 months of incubation. In contrast, monoliths pressed with no prior sonication treatment dissolved and broke easily upon contact with water. For heat-dried monoliths, a considerable shrinking could be observed during drying as water evaporates from the particle network. Comparison of heat drying to a traditional freeze-drying approach as described by [PERSON] et al. [17] showed that the initial size of the wet gel is preserved for the most part (see Figure 5b). However, the stability of the monoliths decreases to a great extent as the particle network could not be further stabilized during drying.