{"id":"5e7ef994-535e-4d21-a22b-5eca4fc6410e","arxiv_id":"2507.16197","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Simulations estimate hydrolysis free-energy barriers for seven Zn-MOFs, showing ZIFs resist water better than IRMOFs and linking barrier height to linker carbon-to-oxygen ratio.","lead":"Researchers used reactive molecular dynamics and metadynamics to estimate how quickly water breaks down seven zinc-based MOFs used in carbon capture, finding ZIFs far more water-stable than IRMOFs. They propose the linker's carbon-to-oxygen ratio as a fast screening metric for designing humid-air-stable MOFs.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quantitative barriers are load-bearing, and the paper's own benchmark (Zn-MOF-74: 13 kcal/mol here vs 22.5 kcal/mol cited from ReaxFF/DFT) suggests the metadynamics protocol is biased; the C/O design rule rests on this unvalidated bias.","rationale":"I read the paper as a transferability study: it applies Yang et al.'s ReaxFF-metadynamics protocol to seven Zn-MOFs and proposes a C/O-ratio heuristic. The qualitative conclusion—ZIFs (Zn-N coordination) are more hydrolysis-resistant than IRMOFs (Zn-O carboxylate)—is chemically plausible, consistent with experimental reports cited in the Introduction, and not the main risk. The risk is quantitative: the screening factor and the timescales in Table 2 are exponential functions of the barriers, and the barriers themselves are the least validated quantities in the paper. The internal Zn-MOF-74 benchmark is the clearest evidence: Section 1 says the single-water barrier is 22.5 kcal/mol from ReaxFF-MD and DFT, and Table 2 reports 13 kcal/mol from the present protocol. That discrepancy is never addressed, and no independent barrier validation is provided apart from comparisons to the originating ReaxFF paper. This is an internal inconsistency, not a disagreement with consensus, and it directly weakens the strongest claim about the C/O design rule. The concern strengthens the reader's conditional verdict, but it does not overturn the qualitative MOF ranking; the correct response is to require validation, not to reject the paper outright. I therefore keep the reader's CONDITIONAL verdict (set as UNCHANGED), with agreement partial: the reader identified force-field transferability and trajectory convergence as the weak assumption, and I add the concrete failing benchmark.","tokens_in":11079,"tokens_out":6629,"duration_ms":67493,"concrete_test":"Run a single DFT-NEB calculation for the same single-water Zn-MOF-74 hydrolysis step on a cluster model with the same collective-variable definition; compare the intrinsic barrier with the 22.5 kcal/mol value cited in Section 1 and the 13 kcal/mol value in Table 2. If the DFT barrier is near 22.5 kcal/mol, the ReaxFF-metadynamics protocol is biased and Figure 4C must be re-derived; if it is near 13 kcal/mol, the discrepancy is resolved and the ranking is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central ranking and design rule rest on seven free-energy barriers. The weakest point is quantitative validity, and the paper contains a direct internal check that is not reconciled. Section 1 cites ReaxFF-MD and DFT values of 22.5 kcal/mol for single-water hydrolysis of Zn-MOF-74, while Table 2 gives the paper's own metadynamics barrier for the same system as 13 kcal/mol—a 9.5 kcal/mol gap, never discussed. Because Table 2's reaction times are computed from Eyring's equation, this gap shifts predicted lifetimes by roughly 10^7, and it falls just in the range separating 'degrades in nanoseconds' from 'stable for hours'. The only external comparisons offered (MOF-177 11 vs 13, ZIF-4 35 vs 40) are to Yang et al.'s ReaxFF work, the origin of the same force-field parameters, so they are not independent validation; Table 1 validates lattice constants, not reaction barriers. A single trajectory per MOF and a manually chosen minimum-energy path on a 2D FES add to the uncertainty. Until the Zn-MOF-74 discrepancy is resolved, the three-point R2=1.0 C/O correlation in Figure 4C is not a reliable screening factor.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript uses ReaxFF-based metadynamics with two collective variables (Zn-water oxygen distance and linker oxygen/nitrogen to water hydrogen distance) to construct two-dimensional free-energy surfaces for hydrolysis of seven zinc-based MOFs: IRMOF-1, IRMOF-10, IRMOF-14, MOF-177, Zn-MOF-74, ZIF-4, and ZIF-90. It reports activation free-energy barriers of 9-19 kcal/mol for the IRMOFs and MOF-177/Zn-MOF-74 and 33-35 kcal/mol for the ZIFs, converts these barriers into first-order reaction times via the Eyring equation, and proposes a linear correlation between the hydrolysis barrier and the linker carbon-to-oxygen ratio (R²=1.0) as a screening criterion for water-stable MOFs. The main conclusion is that ZIFs are substantially more water-stable than IRMOFs, consistent with qualitative experimental expectations, and that non-polar, carbon-rich linkers should be favored for humid CO2 capture applications.","tokens_in":11458,"tokens_out":8688,"duration_ms":85535,"significance":"If the reported barrier ranking is robust, the qualitative conclusion that ZIFs resist hydrolysis much better than IRMOFs is useful and aligns with known experimental behavior, and the low-water-concentration framing is appropriate for flue-gas applications. The paper also shows good lattice-constant agreement with experiment and makes a clear attempt to connect a chemical descriptor (C/O ratio) to stability. However, the quantitative claims are not yet supported: the single-trajectory, manually path-defined barriers lack convergence evidence; the only internal benchmark (Zn-MOF-74) is silently inconsistent with the cited literature value; and the R²=1.0 design rule is fit to three points with no independent validation. As presented, the study is best viewed as a hypothesis-generating computational screen rather than a validated predictive framework. The central qualitative ranking may survive revision, but the descriptor claim and the absolute timescales need substantial additional support.","major_comments":[{"comment":"Section 1 cites ReaxFF-MD and DFT results giving 22.5 kcal/mol for single-water hydrolysis of Zn-MOF-74, and 15.2 kcal/mol for two-water hydrolysis; Table 2 reports this paper's single-water metadynamics barrier for the same MOF as 13 kcal/mol. The 9.5 kcal/mol gap between the cited single-water value and the reported value is never discussed, and the reported value is closer to the two-water barrier. Because the reaction times in Table 2 are computed from these barriers with the Eyring equation, this discrepancy shifts the predicted lifetime by roughly seven orders of magnitude, crossing the boundary between nanosecond-scale degradation and hour-scale stability. This quantitative inconsistency is load-bearing for the stability ranking and must be resolved or the affected claims retracted.","section":"Section 1 and Table 2"},{"comment":"The activation barriers in Table 2 are derived from the highest point of a manually drawn minimum-energy path on a two-dimensional free-energy surface, not from a saddle-point search or committor analysis, and each MOF is represented by a single metadynamics trajectory with no convergence analysis. The quoted uncertainties of ±1 kcal/mol appear to reflect FES resolution rather than statistical error. Without time-dependent barrier estimates or repeated trajectories, the quantitative barriers are not converged. The manuscript should either provide such convergence evidence or explicitly present the barriers as qualitative estimates.","section":"Figure 2C and Section 1"},{"comment":"The central design rule is the linear correlation between the activation barrier and the linker carbon-to-oxygen ratio with R²=1.0. The text and Figure 4C show this correlation for only the three IRMOFs (IRMOF-1, -10, -14), so R²=1.0 is a perfect fit with zero degrees of freedom and carries no predictive power. The two additional ZIF-7/ZIF-8 points in Figure 4A/B come from Yang et al., the source of the same force field, and are not independent. The claim that the C/O ratio 'could serve as a vital screening factor and design criterion' is therefore not established by the presented data; it should be reframed as a tentative hypothesis or tested on independent MOF families.","section":"Figure 4C and Section 2"},{"comment":"The water adsorption energy for ZIF-4 is reported as +28.14 kcal/mol, a positive value that is inconsistent with the negative adsorption energies for all other MOFs in the table and with the text's conclusion that ZIF-90's polar functional group gives stronger water adsorption than ZIF-4. As printed, this internal inconsistency undermines the adsorption-energy discussion. Please correct the sign or the value and ensure the energy convention is defined.","section":"Table 2"},{"comment":"Validation is limited to lattice constants (Table 1), not reaction barriers. The only barrier comparisons in the text (MOF-177: 11 vs 13 kcal/mol; ZIF-4: 35 vs 40 kcal/mol) are against Yang et al. [27], which is the source of the ReaxFF parameters used here; agreement with the source data is not independent validation. To support the absolute barriers and the Eyring-derived timescales in Table 2, the manuscript needs an external check, such as DFT barriers for at least one IRMOF and one ZIF, or experimental activation energies.","section":"Section 1 and Table 1"}],"minor_comments":[{"comment":"The activation barrier for IRMOF-10 is cited as '15±1 kCal/mol (Table 1)' but the value appears in Table 2; please correct the cross-reference.","section":"Section 2"},{"comment":"Reference 37 is garbled ('Lee -h, Demler E et al.') and duplicates reference 33; it should be corrected to the proper author list for Eddaoudi et al., Science 2002, 295, 469.","section":"References"},{"comment":"The red dots representing ZIF-7 and ZIF-8 from Yang et al. are not accompanied by the descriptor values or barriers used to place them, and it is unclear whether they are included in the reported R² values; please specify this in the caption or text.","section":"Figure 4"},{"comment":"The methods state that MD simulations were run for 3 ns, but the FES in Figure 2C is described as 'constructed ... over 600 picoseconds'; clarify the relationship between the total simulation time and the portion used for the FES, and do the same for the SI figures.","section":"Section 1 and Figure 2"},{"comment":"The unit kcal/mol is written as 'kCal/mol' in several places; use a consistent symbol (kcal/mol).","section":"Throughout"},{"comment":"No data availability statement is included; providing input structures, ReaxFF parameters, and PLUMED input files would aid reproducibility.","section":"Data availability"}],"recommendation":"major_revision","confidential_remarks":"The qualitative trend (ZIFs more stable than IRMOFs) is consistent with experiments and likely survives revision, but the quantitative barriers and the C/O ratio design rule are not yet established. The Zn-MOF-74 internal discrepancy and the three-point R²=1.0 fit are the main concerns. I do not see grounds for rejection if the authors add convergence evidence, resolve the Zn-MOF-74 issue, and temper the predictive claims. The manuscript fits the journal's scope well."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague—\n\nThe paper applies Yang et al.'s ReaxFF-metadynamics protocol to seven Zn-MOFs and confirms the known ZIF-over-IRMOF stability ordering with new systems: IRMOF-10, IRMOF-14, ZIF-90, ZIF-4, and Zn-MOF-74. That is the genuinely new content, plus a proposed descriptor—linker carbon-to-oxygen ratio—that correlates with hydrolysis barriers (R^2=1.0) and is offered as a screening rule. The qualitative story is plausible and consistent with experiments, and the lattice-constant validation against experiment is careful.\n\nThe soft spots are proportionate to how much weight the claims carry. The central numbers are free-energy barriers from one metadynamics trajectory per MOF, with no convergence analysis and barriers hand-picked from the FES. That alone would make me cautious. The bigger problem is internal: the paper cites a ReaxFF/DFT barrier of 22.5 kcal/mol for single-water hydrolysis of Zn-MOF-74, then reports its own metadynamics barrier of 13 kcal/mol for the same system, and never discusses the 9.5 kcal/mol gap. Since the estimated lifetimes come from Eyring's equation, that gap shifts them by seven orders of magnitude—the difference between 'degrades in nanoseconds' and 'stable for hours.' The only external comparisons (MOF-177, ZIF-4) are from the same force-field source as the parameters, so they do not validate the barriers independently.\n\nThere is also an internal inconsistency: Table 2 lists a positive water adsorption energy for ZIF-4 (28.14 kcal/mol), which is unphysical, and the conclusion that 'all the MOFs studied are stable at room temperature' sits awkwardly next to the same table's IRMOF-1 reaction time of ~10^-10 hr. The R^2=1.0 C/O correlation uses only three IRMOF points; the ZIF-7/ZIF-8 points added to the C-O bond and charge plots come from the same force-field family and do not make the descriptor an independent prediction.\n\nWho benefits: readers working on hydrolysis of MOFs with ReaxFF, and experimentalists looking for cheap stability heuristics. The paper deserves peer review because it addresses a real bottleneck and the method is reproducible, but it needs major revision—reconcile the Zn-MOF-74 discrepancy, add convergence checks, fix the ZIF-4 adsorption energy, and soften the design-rule claim to a hypothesis. I would not cite it in the next year as a quantitative source.\n\nFor the record: the stress-test note is fair, and the discrepancy it flags is the paper's weakest point. I'd send it to review with the expectation of heavy revision.","headline":"Useful application of an existing ReaxFF/metadynamics protocol to new MOFs, but the quantitative barriers and the C/O design rule rest on unvalidated, single-trajectory data.","tokens_in":11901,"tokens_out":2849,"would_cite":false,"duration_ms":27062,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Hydrolysis barriers in seven zinc MOFs line up with the linker's carbon-to-oxygen ratio.","keywords":["metal-organic frameworks","hydrolysis","metadynamics","ReaxFF","free energy surface","carbon-to-oxygen ratio","water stability","ZIF"],"falsifier":"Calculate the hydrolysis barrier for IRMOF-1 with a converged density functional theory method, or measure its humid-degradation rate as a function of temperature: if the true activation energy is not close to the reported $9 \\pm 1$ kcal/mol, the force-field-based ranking and the carbon-to-oxygen correlation lose their quantitative support.","tokens_in":10860,"feed_emoji":"💧","tokens_out":10620,"duration_ms":104491,"temperature":0.7,"pith_summary":"This paper tries to establish that the hydrolytic stability of zinc-based metal-organic frameworks can be read off the organic linker: zeolitic imidazolate frameworks (ZIFs), which coordinate zinc through nitrogen, resist water attack far better than isoreticular frameworks (IRMOFs), which coordinate through carboxylate oxygen, with computed activation free-energy barriers of 33 to 35 kcal/mol versus 9 to 19 kcal/mol. It further claims that the linker's carbon-to-oxygen ratio correlates linearly with the hydrolysis barrier ($R^2 = 1.0$), making that ratio a candidate screening criterion for water-stable MOFs. If true, the result gives materials designers a cheap, chemistry-based rule for choosing frameworks that survive wet flue gas, a central obstacle for MOF-based carbon capture.","feed_headline":"ZIFs beat IRMOFs on water stability in atomistic simulations","feed_subtitle":"Simulations put ZIF hydrolysis barriers at 33 to 35 kcal/mol versus 9 to 19 for IRMOFs, a cheap screening rule.","key_machinery":"The machinery is metadynamics, an enhanced-sampling molecular dynamics method that gradually fills free-energy basins with bias potentials to map the free energy surface of a rare reaction. The reaction is driven with two collective variables: the distance from a zinc site to the water oxygen ($d_{\\mathrm{Zn-O_w}}$) and the distance from the linker's coordinating atom (oxygen in IRMOFs, nitrogen in ZIFs) to a water hydrogen ($d_{\\mathrm{O_c/N_c-H_w}}$). Hydrolysis barriers are read from the minimum-energy path on the resulting two-dimensional free energy surface and converted into degradation timescales with the transition-state rate equation. The load-bearing identity is the claimed linear relation between the linker carbon-to-oxygen ratio and the hydrolysis barrier, with $R^2 = 1.0$.","core_discovery":"On its own terms, the paper reports free energy surfaces for single-water hydrolysis in seven common zinc MOFs and finds that the rate-determining step is cleavage of the metal-linker bond: Zn–O in IRMOFs and Zn–N in ZIFs. The computed activation free energy barriers are $9 \\pm 1$ kcal/mol for IRMOF-1, $15 \\pm 1$ for IRMOF-10, $19 \\pm 1$ for IRMOF-14, $11 \\pm 1$ for MOF-177, 13 kcal/mol for Zn-MOF-74, $33 \\pm 1$ for ZIF-90, and $35 \\pm 1$ for ZIF-4. The paper attributes the higher ZIF barriers to the less polarizable, stronger Zn–N bond and to the non-polar imidazolate environment, and it shows that adding a polar aldehyde group lowers the barrier and strengthens water adsorption. Its central design claim is that the activation barrier for IRMOF hydrolysis rises linearly with the organic linker's carbon-to-oxygen ratio ($R^2 = 1.0$), which it proposes as a screening factor and design criterion, with the corollary that saturated metal centers linked to non-polar, carbon-rich ligands should be most stable.","pith_inferences":["The paper leaves implicit that its $R^2 = 1.0$ correlation rests on only three IRMOF barriers; a natural extension is to test the carbon-to-oxygen descriptor across a wider set of linkers and mixed-linker frameworks to see whether the linearity is predictive.","The single-water, low-concentration setup is a deliberate limit, but real humid flue gas and liquid water can deliver several waters to one metal site, and cooperative attack could lower the barrier; testing that regime is the clearest extension.","The same metal–ligand bond-polarity argument could transfer to non-zinc MOFs, where the identity of the metal changes the bond strength and polarizability; a two-parameter descriptor combining metal and linker properties would generalize the design rule.","Combining the kinetic barrier with the computed water adsorption energy would yield a two-dimensional stability map separating thermodynamic affinity for water from resistance to hydrolysis."],"forward_implications":["A designer could rank candidate IRMOF linkers for water resistance by computing a single stoichiometric ratio, without simulating the full hydrolysis reaction.","In humid flue-gas separations, ZIF-type frameworks with saturated ZnN4 coordination should outperform carboxylate IRMOFs by many orders of magnitude in lifetime.","Polar ligand functional groups such as aldehydes lower the hydrolysis barrier and strengthen water adsorption, so non-polar or methyl-functionalized linkers are the safer choice for water-stable capture materials.","The transition-state timescales imply IRMOF-1 degrades within nanoseconds while ZIF-4 would persist for roughly a billion hours at 300 K, defining very different operating windows for the two families.","Because the barrier also tracks the number of carbon–oxygen bonds and the metal–ligand charge product, simple bond-count or charge descriptors may substitute for expensive reactive simulations in early screening."],"supporting_citations":[{"why":"Supplies the ReaxFF parameters and the metadynamics strategy, plus prior barriers for ZIF-4 and MOF-177 that this work reproduces.","marker":"[27]"},{"why":"Provides the experimental hydration activation energy for IRMOF-1 used as a benchmark for the computed 9 kcal/mol barrier.","marker":"[21]"},{"why":"Experimental demonstration that ZIF frameworks resist boiling water, the anchor for the claim that ZIFs are water-stable.","marker":"[18]"},{"why":"Prior reactive molecular dynamics study of IRMOF water stability, establishing the method lineage for critical water content.","marker":"[23]"},{"why":"Reports reactive force field hydrolysis barriers for Zn-MOF-74 that the paper compares with its own 13 kcal/mol value.","marker":"[24]"},{"why":"Density functional theory study of MOF-74 water stability used as a cross-check for the reactive force field.","marker":"[25]"},{"why":"Transition-state rate equation used to convert computed free-energy barriers into hydrolysis timescales.","marker":"[43]"}],"fun_headline_variants":["ZIFs shrug off water, IRMOFs don't: hydrolysis barriers 33-35 vs 9-19 kcal/mol","Hydrolysis-free? ZIFs hold, IRMOFs fail: 33-35 vs 9-19 kcal/mol barriers","ZIFs outlast IRMOFs in water: 33-35 vs 9-19 kcal/mol barriers","MOF water stability: linker carbon-to-oxygen ratio predicts hydrolysis barrier"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The entire ranking rests on one atomistic computer model of chemical bonding, and that model's predicted hydrolysis barriers are not checked against experiment or quantum chemistry for most of the seven frameworks; only the crystal sizes are validated.","fun_headline_variants_meta":{"raw":{"variants":["ZIFs shrug off water, IRMOFs don't: hydrolysis barriers 33-35 vs 9-19 kcal/mol","Hydrolysis-free? ZIFs hold, IRMOFs fail: 33-35 vs 9-19 kcal/mol barriers","ZIFs outlast IRMOFs in water: 33-35 vs 9-19 kcal/mol barriers","MOF water stability: linker carbon-to-oxygen ratio predicts hydrolysis barrier"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000883,"raw_usage":{"total_tokens":3842,"prompt_tokens":1000,"completion_tokens":2842,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":616,"completion_tokens_details":{"reasoning_tokens":2730}},"tokens_in":616,"tokens_out":2842,"duration_ms":22443,"temperature":1.0,"reasoning_tokens":2730,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T15:14:54.057421+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Calculate the hydrolysis barrier for IRMOF-1 with a converged density functional theory method, or measure its humid-degradation rate as a function of temperature: if the true activation energy is not close to the reported $9 \\pm 1$ kcal/mol, the force-field-based ranking and the carbon-to-oxygen correlation lose their quantitative support.","supporting_citations":[{"cited_title":"ReaxFF Molecular Dynamics Simulations of Water Stability of Interpenetrated Metal –Organic Frameworks","cited_arxiv_id":null,"evidence_quote":"Supplies the ReaxFF parameters and the metadynamics strategy, plus prior barriers for ZIF-4 and MOF-177 that this work reproduces."},{"cited_title":"Exceptional chemical and thermal stability of zeolitic imidazolate frameworks","cited_arxiv_id":null,"evidence_quote":"Provides the experimental hydration activation energy for IRMOF-1 used as a benchmark for the computed 9 kcal/mol barrier."},{"cited_title":"Characterization of interfacial water in MOF-5 (Zn4(O)(BDC)3) —a combined spectroscopic and theoretical study","cited_arxiv_id":null,"evidence_quote":"Experimental demonstration that ZIF frameworks resist boiling water, the anchor for the claim that ZIFs are water-stable."},{"cited_title":"Effects of water vapor and trace gas impurities in flue gas on CO2 capture in zeolitic imidazolate frameworks: The significant role of functional groups","cited_arxiv_id":null,"evidence_quote":"Prior reactive molecular dynamics study of IRMOF water stability, establishing the method lineage for critical water content."},{"cited_title":"Virtual High Throughput Screening Confirmed Experimentally: Porous Coordination Polymer Hydration","cited_arxiv_id":null,"evidence_quote":"Reports reactive force field hydrolysis barriers for Zn-MOF-74 that the paper compares with its own 13 kcal/mol value."},{"cited_title":"Water adsorption in MOFs: fundamentals and applications","cited_arxiv_id":null,"evidence_quote":"Density functional theory study of MOF-74 water stability used as a cross-check for the reactive force field."},{"cited_title":"The Activated Complex And The Absolute Rate of Chemical Reactions","cited_arxiv_id":null,"evidence_quote":"Transition-state rate equation used to convert computed free-energy barriers into hydrolysis timescales."}],"review_version":1}